You tighten loosen them using the bolts on the alternator... wind the alternator in and it gets looser. Then you should be able to get your hand in there from the top and take the belt off.
Putting on is a bit of a bitch to get it all in the right spot without falling off. start by looping around the bottom then feeding around the power steering and under the guide wheel that does nothing, then go from water pump up and over alternator again... pull alternator so it makes belt tight and boom.
Work on it leaning over the drivers side guard (put a towel there if you are worried about scratches).
Gregories manual definitely has how to do the belts.