How do you photoshop a athlete into a different uniform?

hey guys, I am becoming a huge fan of photoshopping and have a great idea but dont know how to perfect it. My question is how can I change a players jersey (lets say tim tibow florida uniform) to a different teams uniform (to a denver bronco uni) using adobe photoshop. I have seen this on several different magazing covers and such and really would like to learn. Does anyone have any advice or tutorials that can help?