One pulley at a time, starting with the drive pulley under the engine. If your deck has covers on it, those are easy to remove if you have the right torque bit.
BE SURE to MAKE SURE, that the belt is up against the pulleys instead of the guides. There's one pulley that seems to have two little flaps that the best has to go over to make complete contact with the pulley. You can't really see it. You just have to feel for both of them.
If the belt is not on the pulley (and instead of flap), it'll rip the belt up really quick because the flap is sharp.
