They have two mower belts. One drives the belt and the other goes around all the pulleys on the deck itself.
The drive belt has a tensioner release. It is behind the right rear wheel. Pull it back, then down, then release it. You'll feel the spring tension pulling against you. That will remove most of the tension from the deck drive belt (aka primary belt). Then you just remove the belt.
I'd suggest paying attention to how the tensioner works and which side of the belt the pulley is on.
