My dented car - courtesy of my wife

[reno911]

I have taken apart a couple of cars and the fender section is not too overwhelmingly hard to do. Once you have the bumper, headlight, and plastic liners off it is pretty simple from there. Then again that depends on having good access, I.E. a good jack or lifts...

See if you can find a decent Mazda 3 forum. There may be a walk through on the web somewhere showing you how to get that thing off.

edit: place some masking tape on the edges of the new part so whilst installing not to scratch the new part.