Step 1) Ease/prize off the black plastic triangle behind the mirror plate on the inside of the door
Step 2) Undo the three large screws that are revealed
Mirror is now free.
Points to consider...have the door window open so you can hold the mirror or it will probably fall onto the floor when you remove the last screw
Atlernatively, if you just want to remove the mirror and not the plate, there are a couple of screws under the bottom of the plate. I have seen these as both 'normal' heads and spline heads so pay attention.