Hi there I have just changed the one in mine as the thing packed up.
quite simple, the unit is complete, first you need to remove the handbrake gater and remove the screws underneith. then remove the ash tray, to do this there are 2 screws, ash tray will come out, un plug the cable and remove.
2 more screws at the back where the ash tray is need to come out and the centre consol will move back a few CM's thats all that is required.
remove the cd player, make sure you have the code before doing this.
you will now be able to see 4 screws at the top of the heater unit and 2 at the bottom, remove all 4 and the unit will come out, be careful not to pull too hard. remove all cables, replace with new unit and put interior back together.
I found that the stereo unit metal holder got in the slightly, but it bends nice and easy so not too much hassle, test before putting the car back together.
should take approx 40 mins to do the job
Hope this helps a little