It's actually pretty simple. The idler pulley closest to the crank pulley is the tensioner (if you face the crank pulley, it's at about 10:30). Put a box-end wrench on the bolt head that appears to be attaching the pulley, and rotate the wrench clockwise (when facing the engine) -- it'll take about 10-15 pounds of force on the end of the wrench. The whole pulley assembly will rotate toward the passenger side, releasing the tension from the belt. Then, while holding the wrench with one hand, use the other hand to slide the belt off a pulley (doesn't matter which one) and then slowly release the wrench.

Putting the belt back on is the reverse procedure. But it'll be a little trickier, since the belt will try to fall off if you're not careful. If you can get an assistant, that'll make it easier, but it can be done by just one person (it's not a big deal once you've done a few, but the first time can be frustrating).

Good Luck!