Facing the engine from the front, the tensioner is on the left side above the ac compressor. There is another belt for the AC. Don't remember the size but if you look there, there is a pully. I put a 1/2"drive socket (not the bolt size) and rotate counter-clockwise to release tension. and then I slip it over the alternator pulley. To install, I route it everywhere except the alternator, pull the tensioner and slip the belt over the alternator. It is not easy to get it over the alternator as I have to crank on the tensioner and struggle to push it over the alt pulley. New belts are much harder than the old one you pull off.

 

Like stated above, it is alot easier if you take the upper fan shroud off too. Comes of with just a few fasteners.

 

I agree w/ the other guys' suggestions.

I think it is a 5/8" tensioner bolt. I'm not 100% sure. Slight turn counter-clockwise, and it'll come off easy. I've done this three times on my '02 Yukon with the intake and shroud in place. Nothing to it. It's not that bad, but if you feel more comfortable, remove 'em. That'll give you a better look at what's in front.

Side note: you'll have to work the alt off. I used a long-shaft screwdriver to pry b/t the bracket & alt. Install the alt back requires a bit more. There's some sleeves in the bolt holes of the bracket the you may want to work outward a bit before attempting to install a new alt. Once you've done it once or twice, it gets easier.

 

Either will work. Like Bish says, there is a square hole in the tensioner arm that is 1/2". Put your 1/2" drive breaker bar in there and rotate until the tensioner pushes away from the belt and slides off. Just be careful when releasing the tensioner as it travels a LONG way back and can get caught on the shroud and other items.