
First up, there's a bolt in the bracket with its head facing the front of the engine. This is the bolt that is used to hold the alternator in place - ie, the tensioner locking bolt. The first thing you'll want to do is back this off a bit.
Now the really long bolt that goes through the end of the bracket is what is used to pull and push the alternator. Wind it anticlockwise until the alternator cannot be pushed in any more. If you are having difficulty doing this, then either a) loosening the pivot bolt (at the bottom of the alternator) or b) using something long for leverage and pushing against the alternator - may help.
Now slide the belt on, but slide it onto the biggest pulley last. I find that it's easiest to get a tough-to-install belt onto the largest pulley.
Once the belt is done, wind the really long bolt back up until tight, and then wind the locking bolt back into place. If you loosened the pivot bolt, ensure it's tight.