Serpentine Belt Problem

I've got a 97 Cavalier with a 2.2 engine. I need to change the alternator but am having trouble with loosening the serpentine belt.This engine has no tensioner pulley - only an idler pully.
1) How do you go about loosening the serpentine using the idler pulley?
2) What size/type metric wrenches are required?
3) Do I need to take off the top motor mount which is directly over the front of the engine?'
4) What else do I need to know?

Thanks in advance

It has both a tensioner and an idler--- look closer-- much easier to access from underneath and through the wheel well-- use a 15mm wrench to unload the tensioner.....tensioner is below the power steering pump....

otherwise there would be no way to remove belt----unless you consider the new stretchy belt design found on the 2010 Camaro V-8 a/c belt-- which indeed does not use a tensioner...

I know that most of these engines have a tensioner, but this one does not. There is only an idler.

http://partimages.genpt.com/partimages/305600.jpg

you should see this around the center of the engine. It is the tensioner! If it does not move it is frozen (not uncommon) and needs to be replaced. They run about $60.

Thanks Airjer. Would you happen to know what type of tool I'll need and what size socket it requires?

15mm wrench to unload the tensioner.....
...

So, the same size wrench is used on the idler pulley as on the tensioner. Thanks guys.