Exchanging iPhone 5 for a different color?

Currently, I have a white iPhone 5 and I've had it since the 5 came out. I did get a replacement less than a year ago because the home button wasn't working on the first one. I do not want to upgrade to the 5s, but does anyone know what the process is to getting the black one? Is there a fee? If so, how much? Would an Apple store be the best place to do this? Thank you!