Park your lawn tractor on a level surface, and turn off the engine. Lower the deck to your desired cutting height.
Measure the distance between the ground and the bottom of the deck gauge wheels. The bottom of the wheels should be between 1/8 and 1/2 inch off the ground.
Hold the head of the bolt that secures the wheel to the deck flange with a wrench, and loosen the nut with a socket wrench. Remove the bolt and wheel from the deck flange.
Move the bolt to the hole on the flange that allows the bottom of the wheel to be at the correct level. Thread the nut onto the bolt and tighten with a socket wrench. Repeat for the deck wheel on the other side.