Brother Willie shares his battle-scarred experience with replacing these types of refrigerator door gaskets. To summarize in a word: DON'T. Or, if you must because you're a professional Appliantologist, make sure you charge a lot for the job.
Sounds like you have a FIP, (Foamed-In-Place), door liner. I've only had to replace a door gasket on a FIP door one time and probably will not every do it again.
You have to cut the old gasket in four places, (in the middle on each side), and carefully pull the gasket lip straight out from under the plastic liner, being careful not to pull up and break the liner away from the foam.
They you have to make sure the channel is clear of any remaining foam particles with a putty knife about 1/2" in all the way around.
Then the you have to get the new gasket installed, this was the nightmare part. Says to insert opposite diagonal corners first then other two diagonal corners. First two-no problem, third corner-no problem, forth corner - OHHH!!!!! What B!TCH!!!!! It was a real fight to get it to stretch out enough without tearing the gasket to get it over and under the lips of the liner.
But Brothers PDuff and JJ Surfer offer these consoling words of wisdom:
Concur with Brother Willie on the gasket replacement. Attempt only as a last resort. I think if you follow the instruction sheets on those they want you to remove the door to replace the gasket.
FIP gasket aren't that bad to do. The replacement gaskets have a had plastic edge that snaps into channel between liner and door panel. After removing the old gaskets I put silicone caulking where the new gasket will snap into the liner. Two problems with FIP door gasket replacement:
1. If you don't put adhesive the gasket tend to slide, especially on the hinge side where the door cams constantly slide up and down
2. The gaskets often come in too small and need to be stretched, I've done plenty that go on no problem and I have had a lot that seem about 1/4 too short.
Basically the original gaskets are better and should only be changed if there are significant tears, splits or missing magnets.