Start on the inside and take the set screw out that holds the handle in place. Once the handle is off, there are some plastic housings that have to be removed to get at the hardware that holds the antenna in place from the inside. I don't have a clear picture in my mind what that looks like (its, spring clips, cotter pins, nuts, etc.). Once the mechanism has been freed from the inside, you will be able to lift the antenna off of the roof and pull the shaft out of the hole that goes through the roof. There will also be the coaxial cable that goes through the roof in a separate hole. The mount for my antenna was a cast pot-metal affair that was pop riveted into the roof skin. The rivets need to be removed, and this pot-metal mounting plate removed. You will then need a round aluminum patch ~8" in diameter, as I recall, that you will seal and rivet into place with olympic rivets.
Be sure not to step on an endcap while working on the roof, or you can permanently dent it.