I can not remove the headlight assembly by removing the 4 bolts.

If there is enough of room, you do not need to remove headlight assembly. If not remove whole assembly to make it easier to get to. For headlight assembly remove the 2-10mm bolts on top of assembly, there is a 10mm bolt on inside bottom that has to come out. Unplug the wires to assembly. When removing assembly, pull from grill side and wiggle it out. God-Bless! Remove the 3 10mm bolts from assembly.

Open the hood & near the top of the headlight you will see 2 bolts (10mm), remove them. You will notice the whole headlight assembly is loose from the top. Look down into the headlight assembly to the left & you will see another 10mm bolt that connects the outside light fixture. Remove the bolt & that light fixture will fall out (top first). Behind that light fixture you will see your last bolt when you look at the front of the vehicle. Remove it & now the entire light assembly will slide out & give you access to the both high beam & low beam bulbs. Hope this helps.

Read more: http://wiki.answers.com/Q/How_do_you_replace_the_headlight_bulb_located_on_a_1998_GMC_Safari#ixzz25o5cWhZA

very simple remove the front radiator sheild it should have 6 plastic clips on it. if you dont know wat that is its the big black plastic cover right when u pop the hood. u will see a 10mm bolt on the top of the headlamp assembly remove that bolt you will also see a screw on the other side on top of the parking lamp assembly remove the srew after the screw is removed u will b able to slide out the parking assembly after that has been removed u will see one more 10mm bolt holding the headlight assembly in place remove that and the headlight assembly will slide out after it is out unplug the 3 electrical connectors from the back of the assembly remove the assembly. if u flip it over their will be four screws on the bottom of the assembly remove the four screw and take the plastic plate off u will see a steal box that is ur headlight CM remove the two electrical connectors off the box one of them goes to the headlight twist off the headlight waterproof cap and un plug.. should take you no more than 30mins

Remove turn signal assembly (uses a torx 15 driver). This will expose the two 10mm bolts on the one side of the headlight assembly. Remove the plastic front grill (uses a torx 15 driver - there are about 6 screws). This will expose the other two 10mm bolts on the headlight assembly. Remove the four 10mm bolts to remove the headlight assembly and this will allow you access to the headlight you need to replace.

remove 2 10mm bolts attaching top of headlight to the radiator support.

remove plastic clip attachinig headlight to top/front of fender.

remove 5 phillips screws on top of grill.

carefully pull out grill enough to remove 1 10mm bolt attaching headlight to radiator support and use slotted screwdriver or prybar to seperate headlight tab from the bracket that goes under the bumper cover.

with a little effort and wiggling pull out headlight assembly.

You have to basically remove the bumper cover in order to do this.
You will need a 10mm socket with a couple extensions and a phillips screwdriver.
First remove the plastic shield inside the wheel well using the phillips screwdriver.
There are 3 10mm bolts that have to be removed the attach the bumper cover to the fender. The first one is just inside the newly uncovered hole. For the other 2 you will need the extensions. They are located all the way back in the hole beside the headlight assembly. If you look in with a flashlight You will see 3 bolts down in there. One of them will have a 1/2 inch spacer on it. Do not worry about this bolt, it holds the header panel on. The other 2 bolts are the ones you need to remove. Once this is done, if you need to remove the bolts under the hood that hold the bumper cover on the header panel. You should now have adequate movement to move the bumper cover out of the way of the 3 10mm bolts on the headlight assembly that were blocked.

You need to remove the front bumper. Five push clips along the hood line, remove the headlight wipers (if equipped), one T25 screw in the front of each fender well, then two 12mm bolts under the headlights (1 each side). Then there are 4 10mm bolts holding the headlight in.

You have to basically remove the bumper cover in order to do this.
You will need a 10mm socket with a couple extensions and a phillips screwdriver.
First remove the plastic shield inside the wheel well using the phillips screwdriver.
There are 3 10mm bolts that have to be removed the attach the bumper cover to the fender. The first one is just inside the newly uncovered hole. For the other 2 you will need the extensions. They are located all the way back in the hole beside the headlight assembly. If you look in with a flashlight You will see 3 bolts down in there. One of them will have a 1/2 inch spacer on it. Do not worry about this bolt, it holds the header panel on. The other 2 bolts are the ones you need to remove. Once this is done, if you need to remove the bolts under the hood that hold the bumper cover on the header panel. You should now have adequate movement to move the bumper cover out of the way of the 3 10mm bolts on the headlight assembly that were blocked.

1/Remove bumper under tray.
2/ " the front of both inner wheel liners.
3/ " a 10mm bolt at top behind both marker lights.
4/Remove 2 10mm bolts above both headlight assemblies.
5/Cautiously withdraw bumper then disconnect bumper harness.

I know your frustration! I cannot believe the complexity of changing the headlights. Chevy has tried to make this a dealer item only just to change a headlight bulb. I will try to explain the procedure unfortunately I do not have photos. First you will need to remove the wheel well liner (two bolts and two plastic push pins). Pull the wheel well housing back (you will need to turn the wheel/tire to gain access) and using a 7mm socket remove the plastic support piece that holds the bumper in place (two bolts). Pull the corner of the bumper down until you can locate the bottom bracket of the headlight assembly that is held by a 10mm bolt. Remove it. (Oh did I mention this is a two person job!) Next move to the front of the vehicle (hood up) and remove all the 10mm bolts holding the upper part of the grill (I think there are eight of them). Now remove the obvious top two bolts on the headlight assembly! With two people - one to work the headlight assembly and one to push down the bumper and pull out on the grill assemble, slowly and carefully pull the headlight assembly straight forward. You will need to be mindfully of the small tabs on the headlight assembly that like to get caught on bumper/grill. If you are just replacing the bulb, you should be able to move the headlight assemble far enough forward to gain access to the bulbs without totally removing the headlight assembly. What a ***** job! SHAME on GM.