If your talking about the aerial mast, it just unscrews off the base.
If your talking about the mast & base, then you need to remove your interior light that's situated on the roof, I think there are 2 screws located underneath plastic caps.
Let the light drop down and hang by it's wires. If you have a sunroof then you will need to remove the sunroof motor that you will see after removing the light, this is a bit more tricky, especially when re-fitting.
After removing the above mentioned, you will see a metal cap, prize this off with a flat screwdriver and underneath this you will see a nut that you unscrew to remove the aerial!
Hope this helps!
