uhoh.... Don't cut your garage!
You need to twist the antenna off (it has a screw at the bottom of the antenna which goes into the black base that is attached to the roof)
You will see the base, then a fat bit of antenna, then a thin shaft, then a plastic cap (the top of the antenna)
Grab the fat bit of the antenna and unscrew it from the base.
It's so easy, there's nothing to it (why do you think it's so easy for kids to nick our antennas?)
Just unscrew the antenna, heat up the top plastic cap and remove it, cut the thin bit to the desired length, put the plastic cap back on, screw the antenna back on, look really happy
