To replace a driver's side mirror you have to first take the door panel off. The majority of the screws holding it on are torx screws. Once the panel is off the mirror has a plug that needs to be unplugged (if it's a power mirror). Then simply unbolt the mirror from the door which should be a 10mm socket, take it off and simply reverse the steps when putting on the new mirror.
Actually, you don't need to take the door panel off. The triangle plastic piece just clips into place. Pull on it gently but firmly and you'll have access to the mounting hardware. Just replaced mine and it took less than an hour. I purchased mine from anythingauto.com and rec'd it 2 days.