It should be easy but as said it is likely the central stud turns and then you need a torx in the middle to stop it.. but the torx is not strong enough. I ended up taking an angle grinder to the nut but that means you need a new nut. It is a standard metric thread so you may have one lying around like me (M14??) with a washer but you should still get a new offical nut as it has a sprung collar and nylock centre so is a bit special.. not sure I ever did replace mine although I did buy a new nut. The Audi dealer ended up selling me the nut for about £2.
This was on a 2005 50k miles car..