First, unplug the refrigerator or shut off the circuit breaker for the refrigerator.
Pull the gasket out of the track. Starting at one of the corners is usually easiest. You may need to tug the gasket firmly to get the removal process started. If you have a difficult time starting at a corner, pull the gasket out starting in a spot halfway down the side of the door.
Once you get the removal process started, you should be able to pull the gasket out fairly easily.
If you're replacing the gasket on the door with the flipper mullion and the mullion blocks door gasket removal, remove the flipper mullion.
Remove the mounting screws from the center mullion bracket.
Lift the mullion up slightly and release it from its top and bottom mounting brackets.
Pull the mullion out slightly and disconnect its wire harness.
Set the flipper mullion aside while you replace the door gasket.