Jobs a fish its really easy to do like Joe says. The only tricky bit is getting the wiper arm of the spline. In the end i just got some mole grips on it and shut my eyes.
It makes the back of the car look so much better i was quite surprised.
And before the PC brigade start
I do low miles but regular washing so i have only used it once, and i am sure i wont miss it.
Also VW gifted me two other mirrors to use if by a freak of nature i decide to not love my car anymore and dont wash it.