Even if you don't have a car, or even drive, knowing how to change a tire is an important life skill. You could be on a drive with friends, or maybe somebody you know will need a little help. And, fair or not, if you're the only guy on the trip, chances are good that everybody will expect you to figure it out because you're a guy.
I was going to type out a step-by-step guide, but there are some really great guides on the Internet already. One with a lot of detail, and some great pictures, is on Popular Mechanics. It's pretty detailed, so if you want something a little simpler, check out "How to Change a Tire for Dummies".
If you're still not sure, or are the kind of person who learns with a little hands on experience, call a local tire or auto parts store. Most of the guys working there could change a tire in their sleep, and you may find somebody who would be happy to walk you through it.
I'm a gay father with gay sons. My mission is to work with the community to prepare them -- and other young gay men -- for a happy and successful life.