See this X5world Article for details on how to do this.

On the bottom portion of the tweeter speaker that is mounted on the door there is a small black tab. Use a small flat blade screw driver to release the tab and remove the speaker grill cover enough to access the 3 bolts holding the mirror in place.

Two of the bolts are located behind what looks like a triangular sponge and the third is behind a rubber gromet in the door jamb.

Trace out the the mirror harness and unplug any of the leads that are connected to the mirror. If there are wire ties, these will need to be cut.

Next, using a T25 or T30 and a ratchet remove the 3 bolts and carefully remove the mirror from the vehicle.

You will be reusing parts of the old mirror on the new mirror, so begin disassembly of the mirror components and the reassemble them in reverse order on the new mirror unit.

Once the mirrors have been reassembled then they are ready to be put back on the vehicle. Doing so requires that the wiring harness be fished back into place and the mirrors bolted back into position. Do not worry if the new mirror mountings do not appear to be threaded. Once you install the mirrors the bolts will self-tap and make new threads in the mirror assembly.

Secure the harness with new wire ties and ensure that all the connections are solid.

Simply follow the disassembly steps in reverse order and be sure to use the new window switch module instead of the new.