Things you'll Need
Screwdriver (May be regular phillips or you may need a special one)
Different color back or front housing

How to do it:
First, you'll need to unscrew the two screws located at the bottom of the phone by the charging port, then the back slides right off
Then you'll easily be able to slide the new back housing in no problem
Re put on the screws and bam, you're already done

here's a video demonstrating how to do it