It is actually really pretty easy to do yourself. I put new speakers in my 2001 SL. What year and model is your friends car? All I did was take off the door panel by removing all the screws and the window handle. Removing the window handle is the toughest part because there is a little C clip holding it on, just use a flathead screwdriver to pop it off and don't lose the clip. You also have to unclip two rods from the door handle and slide them out, after that pull off the door panel and the speaker is right there to change. I am pretty sure that the speakers are 5" 1/4 too, but check
www.crutchfield.com to be certain.