Drive the 11/36 onto flat ground, set the parking brake and disengage the PTO lever. Doing so stops the mower blades and increases slack in the belt for easier removal.
Locate the deck lever on the side of the mower and lower the deck to the position closest to the ground.
Hold on to the PTO pulley, which you can locate under the engine with one hand, and rotate it while you pull the belt off the pulley with the other hand.
Pull the PTO belt off the deck's pulleys. You will locate two spindle pulleys and one idler pulley. Routing is relatively simple, but make sure you install the new belt with the proper routing around the pulleys.
Pull the belt to the front of the mower and wrap it around the PTO pulley. If the belt is too tight to get around the PTO pulley, have a second person push the idler pulley away from the belt to create additional slack.