Can someone explain to me how to change my serpentine belt?

Also, on the advice of the salesperson at AutoZone, I bought the (most expensive) Goodyear Gatorback belt ($35). He claimed that it grips better, which would keep the engine cooler, among other things, as well as possibly improve my gas mileage. I'm not sure I bought his whole sales pitch, but I have heard that the Gatorbacks are really good belts, so I went for it. Is there any major difference between that belt and the Valuecraft ($8) economy version?