The shark fin is held into your roof with a type of adhesive very similar to urethane glue. You need to cut it out very carefully not to a scratch anything. The fin is plastic and under it is the actual antenna which is screwed on with a single screw. I think it's a T27 or T25. We have done a few of these and it requires patients and I recommend it should be don't by professionals.
I'll make a video next time we do a roof and post it up.