Remove all the screws on the top plate except the ones holding the clamps in place. Pry up the top plate on all sides, then lift it off the printer

Rotate each motor pulley until the grub screw is facing up, and tighten. If you don't have the allen wrench that came with your kit, you'll need a metric allen wrench set to do this. There should be two grub screws in each motor pulley and the end of the pulley should be close to flush with the end of the stepper motor shaft.

Tip: Before you put the top back on (and I'd wait until you were done with all the maintenance before you did), tape or hot glue the nylon locknuts into place where the screws from the top plate come down. That'll keep them from popping out when you push the top plate back into place.