Hi there:
I haven't removed the side mirrors on my car, but I have done a lot of R&R on the doors and panels. I believe you will have to completely remove the door panel to access the 2-3 nuts holding the mirror on. Once you remove the door panel, you can pull the plastic window trim (which includes the small speaker grill) up out of the way and get to the nuts. Then just unplug the mirror harness and install your replacement. Just make sure the new mirror is snug before installing everything or you will be doing the job twice.
Also, don't just tear into the door panel removal without consulting the factory service manual or you will break things or chew it up and it will be an eyesore forever.
Good luck.
Psst... before you get over your head, you should download the factory service manual (FSM) at
http://www.phatg20.com and also do some free searches on this site as different projects come up -- and trust me, they will.
Ted