R & R antenna help please

I have a 1992 325ic. The rubber grommet around the antenna is bad. I bought a new one from BMW, but how do I remove and replace it? Do I have to remove the whole antenna and are they’re any trick to doing that? Thanks Dave

The whole unit comes out from the bottom. Haven't had to do it myself, but i played with the motor a bunch to fix it. If i remember right you have to unscrew the motor housing from inside the trunk, and then push it up to remove the exterior collar. Looks easy, but like i said, I haven't done it. The motor is easily accessed after removing the trunk interior liners.