Here's the steps

Remove the trunk floor panel and the left and right trunk side panels. Remove the spare tire. If you have a 4.6iS, remove the spare tire cover and the spare tire.

Remove the black round cover by loosening four (4) 10mm bolts. Then remove the forward and rearward fasteners from the spare tire bracket by loosening two (2) 13mm nuts and two (2) 13mm bolts.



Remove three (3) screws from the battery access panel cover (aka battery module panel) and remove it (the one with the big BMW logo).



After the battery module panel is removed, you will see the black plastic compartment right underneath it. Remove four (4) small screws from the plastic compartment to remove it.



Once this unit is out you can unplug the old radio module (the unit on the left in the picture above, just below the battery), disengage it from the plastic compartment and replace it with the new radio module.

Reverse the steps to reinstall