This is the wierd connector behind the radio. You need to pull it "up" (up being relative to the radio as it normally sits in the car). As you pull this thing "up" it will force the receptacle out of the back. This is all, basically, an excellent example of german over-engineering. The purpose is to get the big plug out of the back of the unit. You can then simply pull the antenna off and unscrew the bullet (anti-theft) cover