It should still be under warranty. Timing belts last 100,000+ miles. Otherwise, it's tricky--if you get even one tooth off the car will run like a lawnmower.
Not to sound rude or anything, but if you need to ask it's best left up to the pros. I was an auto mechanic for 6 years and I can tell you that if a belt isn't done exactly as it should be you can cause serious motor damage. If you are one tooth off or have improper tension the valves can crash into the pistons. If you really want to know how, have a mechanic friend help you out and show you what to do and why.