If it'* bad, cut it off with a pocketknife.
If it'* not, put a 15MM socket on a breaker bar and push the tensioner (In the middle of all the hardware) towards the firewall.
If you're changing the belt, cramp the front wheels to the right, remove the splash guards inside the wheel well, and remove the sleeved motor mount bolt (18 MM) to slip the new belt in. I had a bit of trouble getting the sleeve back in, so I ground a few thousands off the end of the sleeve on my grinder (hold the end flat against the SIDE of the grindstone) and that worked quite well.
Have a helper hold the tensioner forward while you align the new belt on the pulleys. Release the tension, ensure that the belt is perfectly aligned in the grooves, reinstall the splash guards, and you're done.
Took me about 1/2 hour. The belt was $24 at Autozone. Your car should have a diagram under the hood showing the belt routing.
1999 SLE K engine