Replaciing serpentine belt on 2006 Toyota Corolla

You'll have to remove the engine cover under the bottom so you can position the new belt on the pulleys properly. Get a wrench or tensioner tool and turn the tensioner clockwise to relax the drive belt. Don't apply excessive force.

It's hard to draw a picture with words, but looking at the engine from the passenger side of the car, there are basically two top pulleys, two middle, and two bottom. The drive belt goes around the outside of the two top and two bottom, and on the inside of the two middle.