I need to know how to change he door seal(gasket)

1. Buy a gasket that fits your door exactly.
   
2. Soak the new gasket in hot water in the sink to make it pliable.
   
3. Make sure the refrigerator is level.
   
4. Find a nut driver that will fit the screws holding the old gasket in place and lay out your tools where you'll be able to reach them.
   
5. Start at the top outside corner of the door and fold the old gasket back as you partly loosen the screws along half of the top and side. Don't loosen them all the way.
   
6. Pull the old gasket out.
   
7. Attach the new gasket by pushing it beneath the metal retainer and tightening the screws as you go.
   
8. Replace each section the same way.
   
9. Shut the door and check for gaps. The seal should lie straight and smooth all the way around the door.
   
10. Notice if there are gaps between the gasket and the frame - this may indicate that the door has warped. (Fix it by loosening the screws and twisting the door a little. You may have to do this a few times before you get the door straight.)
    
11. Put a flashlight in the freezer pointed toward the opening and shut the door. Turn off the lights. You shouldn't see any light leaking through.
    

Its simple vendor helps you on this topic,Line4line also supplies products such as Wall Anchors and Security Ground Anchors which cater to the need of the clients as per their customized design and the technicality of the project.

http://www.line4line.com/Line4Line/en/24-ladder-brackets

Check this nites as right procedure, even with any variations...

Pre-Installing Tips for Magnetic Gaskets
* Wipe off the cabinet area surrounding the gasket and any food stuck under your old gasket.
* Make sure the new gasket is at room temperature before removing it from the package.
* When handling the gasket, carry it by the corners to make sure that there is no damage done to the internal magnetic tape.
* If your rerfrigerator is using a three sided magnetic gasket, always install the new gasket as the old gasket was removed.

Removing and Installing Tips (Magnetic Gaskets)
* Before removing your old gasket, take a look at how it is secured. You can do that by pulling back on the edge of the gasket.

Method A (Retainer Mount)
1. If metal retainers are used, loosen the screws across top and half way down each side. Don't loosen the screws too much. Just enough to allow the gasket to be pulled out of the retainer. Begin removing the gasket starting at the top, then each side showing where the screws are still secure.
2. Start installing the new gasket at the top by sliding the lip of the gasket under the retainer until you reach the point at where the old gasket is still attached.
3. Tighten the screws onto the new gasket up on top and on the sides. Leave about 2 screws untightened to the old gasket.
4. Loosen the rest of the screws to the old gasket and remove it.
5. Finish installing the new gasket.

* After you finish installing the gasket, close the door to check for alignment. If you need to re-align the gasket, slightly loosen all the screws and flex the door in opposite direction to assure proper door seal contact when closed. When the aligment is right, grasp edge of door about mid-way and slowly open door as to not warp. Re-tighten all of the screws.
* On some doors the hinge side seal might start to roll as it closes against the cabinet shell. If that happens, petroleum jelly is used on hinge side of the gasket surface to help the gasket slide into place. It can also be applied to the gasket to help with this problem.

Method B (Panel Mount)
1. If metal retainers are not used, the above steps can be followed. However, the screws or clips have to be removed as opposed to lightly loosened on the retainer mount style.
2. Replace the gasket the same way discussed above by removing the old gasket from the top and installing the new gasket without fully removing the old gasket.
3. Loosen the rest of the screws to the old gasket and remove it.
4. Finish installing the new gasket.

Installing a Non-Magnetic Gasket
* Non-Magnetic gaskets designs are used on mechanical latch type doors. Follow the same installation methods as A or B.



Remeber to allow the new gasket to reach room temperature before removing it from the pacakage and always carry it by the corners to avoid breakage of the magnetic tape.

Restoring Deformed Gaskets
If you find your gasket to be deformed from storage, you can correct it by applying heat to the deformed sections. Some things you can use are as follows:
* Hair dryer
* Electric heater
* Light bulb (150-300 watt)
* Pan of hot water

Move the source of heat back and forth over the deformed part of the gasket to make sure there is even warmth. Be sure to maintain a distance of 3 to 4 inches between the gasket and the heat source. Keep applying heat until the gasket gets back to its original shape. Using your hands to reshape the gasket can help too.

Also, could check this links for other references: DIY-Projects//how-to-replace-a-refrigerator-door-gasket

Hope helps.