How do I loosen the tension on the tensioner of my 2004 Hyundai Santa Fe to change my serpentine belt?

There is a 3/8" square opening on the pulley end of the tensioner. You will need a 3/8" drive wrench, a handle extension (cheater pipe) and maybe a short (1") entension depending on your wrench. There is alot of tension (which is why you will need the handle extension) and not much room to work; keep the wrench seated against the tensioner or it will break off the aluminum surrounding the opening. I used a block of wood between the wrench and the fender inner liner to keep the wrench head in place. The tensioner moves only a small distance so all you can do is slide the belt off one of the blind pulleys and then slowly release the tensioner. A helper is a good idea.