Prise off the triangular plastic trim on the inside of the door. there are 3 hex head screws holding the mirror assembly to the door.
If it's just the mirror glass you want to replace and not the whole housing/assembly, you can prise the glass away from the plastic clip which it is mouted on by using a screwdriver (carefully) on the short side of the glass. New glass just presses back onto clip (on swivel).
JD, January 2009