I did mine but I have an A3 so not sure for you guys.
There are map lights at the back of the car for the passengers.... pop that panel out - easy peesy. Then you will see a bolt that holds the aerial base to the roof. unscrew that, that part was a bit of a pain as I was not using the right tools but anyhows.... once that's off, the rest is plain sailing. Swap the old base for the new and Robert's yer mothers brother.
Tip....
When tightening up the bolt... either get someone to stand at the back and keep an eye/hold the base so it does not mis-align or like what I did... put bolt back on.... tighten, go out check, then tighten again, check again etc etc.
Maybe that will help ya's. About 15 mins to do I reckon.
Baz