A lot of people are skeptical of changing their own speakers, and instead go and play hundreds of dollars to have a car audio shop do it. Well i'm here to tell you that it's not as hard as it seems! The only background information you need would be how to remove your door panels. You don't know how? LOOK IT UP! After that it's a matter of matching the size of your stock speakers with your new ones. The last relatively difficult part is connecting the speakers. To do that, you have to cut your stock speaker wires, strip them about half an inch and splice on your connectors.
Crutchfield.com does a wonderful job of supplying you with everything you need (tools and information) to replace speakers and other stereo components in your car!