To replace your side mirror you need three parts. The mirror assembly, which includes the motor attaches to the A piller. The lens, which is the glass part that may include dimming/heating. The cover cap, which comes primed but will need to be painted.
Be sure to get the right mirror assembly, there are different versions for if you have shadowline, memory settings and dimming. It's very easy for someone to order the wrong part - double check it!
There is a slight possibility of removing the tweeter without removing the interior panel, but the panel is not that hard to deal with.
Remove the interior trim strip (green) by starting from the side nearest the engine. Pull it gently with your hands and it should come out freely. I did not have much trouble removing the trim strip as the other person did in the e90 guide.
Remove the handle cover (blue) by pulling at it from the bottom area that has been revealed since you removed the trim strip.
There are five screws to remove (yellow) - use a T15 bit to remove them. The screws are quite long.
After the screws are removed, starting from the bottom, pull the panel away from the door carefully. the e90 guide suggested a screwdriver and i slipped a credit card into the gap and used that to lever it out so the screwdriver would not damage the leather. there are plugs that go all along the outside of the door and you have to pop them all out.
When removing the panel, be careful not to yank the door lock plug out or any of the electrical plugs. Remove those by hand.
Remove the tweeter by pulling it straight out. The green arrow is pointing to the tab that holds the tweeter in.
Pull back the rubber strip and remove the three bolts (orange) but be sure to hold up the mirror to prevent it from falling. Remove the blue electrical plug.
Reverse all the steps to install the new mirror assembly. Afterwards, install the lens by snapping it in place (blue), and install the mirror cap by sliding it on (green) carefully being sure not to break the tab at the bottom.
Thanks go out to txusa03
for his e90 outside mirror guide
which I used to come up with this e92 guide.