Ge Spacemaker microwave - Model # JNM1851

That's covered on pages 35 & 36 of your owner's manual.

If for some reason you don't have yours, you can download it here.

Cooktop Light/Night Light

On models JVM1850, JNM1851, DVM1850 and
EMO4000, replace the burned-out bulb with a 120 volt,
40-watt incandescent bulb (WB36X10003), available
from your GE supplier.

On models JVM1870, JVM1871, JVM2050 and
JVM3670, replace the burned-out bulb with a 120 volt,
20-watt halogen bulb (WB36X10213), available from
your GE supplier.

To replace the bulb(s), first disconnect the
power at the main fuse or circuit breaker panel
or pull the plug.

Remove the screw at the left edge of the light
cover and push on the right edge of the cover
to open.

Be sure the bulb(s) to be replaced are cool
before removing. After breaking the adhesive
seal, remove the bulb by either gently turning
(for models JVM1850, JNM1851, DVM1850 and
EMO4000) or pulling straight out (for models
JVM1870, JVM1871, JVM2050 and JVM3670).

Replace with the same size and type bulb.

Raise the light shield and replace the screw.

Connect electrical power to the oven.

Oven Light

Replace the burned-out bulb with a 120 volt, 20-watt
halogen bulb (WB36X10213), available from your GE supplier.

To replace the oven light, first disconnect the
power at the main fuse or circuit breaker panel
or pull the plug.

Remove the top grille by taking out the screws
on top of the grille that hold it in place and
sliding the grille to the left (opening the door
makes grille removal easier).

Next, remove the light cover.

On some models, the light cover is located
in the center of the top opening. Remove the
screw that secures the light cover and lift the
cover off.

On some models, the light cover is located at the
left of the top opening. Lift the cover off.

Pinch the clips that hold the light socket in
place and lift the socket out.

Remove the bulb from the light socket by
pulling straight out. Replace with the same size
and type bulb, then replace the light socket and
cover.

Replace the grille and screws. Connect electrical
power to the oven.

We're happy to help you with free advice and we'd appreciate your thoughtful rating of our answer.

That's on page 33 of the owner's manual. If you've misplaced yours, it's archived online here.

Cooktop Light/
Night Light

Replace the burned-out
bulb with a 40-watt
incandescent bulb
(WB36X10003), available
from your GE supplier.

1 To replace the bulb(s),
first disconnect the power
at the main fuse or circuit
breaker panel or pull the
plug.
2 Remove the screw from
light cover and lower
the cover.
3 Be sure the bulb(s) to be
replaced are cool before
removing. After breaking
the adhesive seal, remove
the bulb by gently turning.
4 Replace the screw.
Connect electrical power
to the oven.

Oven Light

Replace the burned-out
bulb with a 40-watt
incandescent bulb
(WB36X10003), available
from your GE supplier.

1 To replace the oven light,
first disconnect the power
at the main fuse or circuit
breaker panel or pull the
plug.
2 Remove the top grille by
taking out the 2 screws
that hold it in place.
3 Next, remove the screw
located above the door
near the center of the
oven that secures the
light housing.
4 Replace the screw.
Connect electrical power
to the oven.

We're happy to help you with free advice and we'd appreciate your thoughtful rating of our answer.

That's covered on pages 35 & 36 of the owner's manual here.

Cooktop Light/Night Light

On models JVM1850, JNM1851, DVM1850 and
EMO4000, replace the burned-out bulb with a 120 volt,
40-watt incandescent bulb (WB36X10003), available
from your GE supplier.

On models JVM1870, JVM1871, JVM2050 and
JVM3670, replace the burned-out bulb with a 120 volt,
20-watt halogen bulb (WB36X10213), available from
your GE supplier.

To replace the bulb(s), first disconnect the
power at the main fuse or circuit breaker panel
or pull the plug. *

Remove the screw at the left edge of the light
cover and push on the right edge of the cover
to open.

Be sure the bulb(s) to be replaced are cool
before removing. After breaking the adhesive
seal, remove the bulb by either gently turning
(for models JVM1850, JNM1851, DVM1850 and
EMO4000) or pulling straight out (for models
JVM1870, JVM1871, JVM2050 and JVM3670).

Replace with the same size and type bulb.

Raise the light shield and replace the screw.
Connect electrical power to the oven.

Oven Light

Replace the burned-out bulb with a 120 volt, 20-watt
halogen bulb (WB36X10213), available from your
GE supplier.

To replace the oven light, first disconnect the
power at the main fuse or circuit breaker panel
or pull the plug.

Remove the top grille by taking out the screws
on top of the grille that hold it in place and
sliding the grille to the left (opening the door
makes grille removal easier).

Next, remove the light cover.

On some models, the light cover is located
in the center of the top opening. Remove the
screw that secures the light cover and lift the
cover off.

On some models, the light cover is located at the
left of the top opening. Lift the cover off.

Pinch the clips that hold the light socket in
place and lift the socket out.

Remove the bulb from the light socket by
pulling straight out. Replace with the same size
and type bulb, then replace the light socket and
cover.

Replace the grille and screws. Connect electrical
power to the oven.

We're happy to help you with free advice and we'd appreciate your thoughtful rating of our answer.

* If your control board was damaged (lights won't come on, won't go off, fan or turntable not working right) after a cooktop light bulb blew or was inserted or removed while power was on, see here.

There should be a panel covering the bulb iside the cookspace with a screw holding it on. Remove screw, cover then bulb.

From the owner's manual:

Cooktop Light/Night Light

On models JVM1850, JNM1851, DVM1850 and EMO4000, replace the burned-out bulb with a 120 volt, 40-watt incandescent bulb (WB36X10003), available from your GE supplier.

On models JVM1870, JVM1871, JVM2050 and JVM3670, replace the burned-out bulb with a 120 volt,
20-watt halogen bulb (WB36X10213), available from your GE supplier.

To replace the bulb(s), first disconnect the power at the main fuse or circuit breaker panel or pull the plug.

Remove the screw at the left edge of the light cover and push on the right edge of the cover to open.

Be sure the bulb(s) to be replaced are cool before removing.

After breaking the adhesive seal, remove the bulb by either gently turning (for models JVM1850, JNM1851, DVM1850 and EMO4000) or pulling straight out (for models JVM1870, JVM1871, JVM2050 and JVM3670).

Replace with the same size and type bulb.

Raise the light shield and replace the screw.

Connect electrical power to the oven.

Oven Light

Replace the burned-out bulb with a 120 volt, 20-watt halogen bulb (WB36X10213), available from your
GE supplier.

To replace the oven light, first disconnect the power at the main fuse or circuit breaker panel or pull the plug.

Remove the top grille by taking out the screws on top of the grille that hold it in place and sliding the grille to the left (opening the door makes grille removal easier).

Next, remove the light cover.

On some models, the light cover is located in the center of the top opening.

Remove the screw that secures the light cover and lift the cover off.

On some models, the light cover is located at the left of the top opening.

Lift the cover off.

Pinch the clips that hold the light socket in place and lift the socket out.

Remove the bulb from the light socket by pulling straight out.

Replace with the same size and type bulb, then replace the light socket and cover.

Replace the grille and screws.

Connect electrical power to the oven.

We're happy to help you with free advice and we'd appreciate your thoughtful rating of our answer.

how do I change the little light bulb on the top to take off the cover what do i need.

Please, [email protected]

Here is the GE download page for your manual. Page 35 of your  manual gives the light bulb replacment instructions. 

http://genet.geappliances.com/DocSearch/Dispatcher

That model number doesn't look quite right, but nevertheless:

If there's no obvious removable cover over the bulb (and the owner's manual doesn't address it) some disassembly may be required.

Always unplug a microwave before removing or installing any bulbs.

If it's an over the range type, remove the vent grille across the top and see if bulbs can be accessed there. There may be a panel on the bottom covering the light(s), instead.

If not, chances are you'll have to remove it from the wall, then remove the outer cover. If so, the installation instructions are very handy, and it's best to have two people since the microwave can be heavy and awkward.

Once it's out of the wall, the outer cover (wrapper) will need to be removed, just as you'll need to do on a counter top model.

On a counter top model, be sure it's unplugged, but otherwise ignore the instructions above this paragraph.

The screws you need to remove should be pretty obvious, but a special driver (such as a T20H Torx type or GTXH20-100) may be needed.

Be sure to put all the screws back in the right holes, since some may be special grounding screws.

Bulbs can be had in most grocery stores, hardware stores, home improvement centers, and big box or department stores.

Many models use halogen lamps. You must not touch the new one with your bare skin, as the oils will shorten the bulb life.

We're happy to help you with free advice and we'd appreciate your thoughtful rating of our answer.

Your post has two distinct model numbers shown, so it's hard to be precise, but I'll try my best.

You can usually find helpful exploded view diagrams and order parts by entering your full model number here: http://tinyurl.com/gv383

I have a diagram at my site which helps you find & replace many GE cooktop and cavity light bulbs. Other models are similar. It's at
http://207.234.249.73/mwd/ge_lamp_replacement.jpg

Always unplug a microwave before removing or installing any bulbs!

If it's an over the range type, remove the vent grille across the top and see if bulbs can be accessed there.

There may be a panel on the bottom covering the light(s), too.

If not, chances are you'll have to remove it from the wall, then remove the outer cover.

Many models use halogen lamps. You must not touch the new one with your bare skin, as the oils will shorten the bulb life.

If yours is an Advantium type, the following instructable should help: http://www.instructables.com/id/SZFF4WSF44XYT8X/?comments=all

We're happy to help and we appreciate your thoughtful rating of our answer.

The interior oven light can be accessed in the following way:
1.Open door and remove the top grill via the 2 screws along the top edge.
2. In the interior light will be under metal plate with fasten by single screw. The halogen bulb is rated at 120V 20watt. Looks like a G-8 bulb with 8mm pin spacing with o.a.l. 1-5/8" long

Get these bulbs cheap at http://www.1000bulbs.com/120-130-Volt-G8-Base-Halogen-Light-Bulbs/