Here is a picture of how one can try removing a Antenna Nut from the outside of your car.  To remove the nut, turn it off Counter Clock wise, looking down at it.  Extreme care should be taken when doing this, don't hit it hard, just light taps, as you don't want to slip.    If you have a nut with round holes, take a small needle nose pliers and put the ends in the holes and turn.