Different makes and models install differently. Please ask again with the make and model.
you were no help
Remove the mower deck. Block the blade from turning by using a piece of wood wedged between the blade and the mower deck. Loosen the nut on the top of the pulley (May require a cheater bar). Remove the pulley. If it doesn't come off easily, use a 3 armed pully remover. Once the pulley is removed, loosen the four self-tapping bolts that hold the spindle to the bottom of the deck and the spindle will fall loose. Remove the blade. Install the new spindle from below using NEW self-tapping bolts to bolt the new spindle to the deck. Replace the blade, install pulley, block blade from turning then tighten the top nut.
you probably have a bad bearing
Remove the deck. First by pulling the pins that attach the lift brackets, and then remove the rear spring, and the 2 belt guides under the engine for the belt that drives the deck (1/4" socket). After the deck is out, release the spring that applies tention on the right idler pulley (you'll have to remove the 2 side pulley covers).
As your sitting on your mower look down on your left side on the deck is a metal arm locked under a hook get off the mower push down on the arm and pull out toward the rear tire this loosens the rear pulley now put belt over the top front pulley and over the rear pulley move metal arm back to hook and lock in place then your done.
The front snowblower attachment on the GT225 is powered by the engine through a belt that extends to the pulley on the bottom of the engine. ( it is the same pulley that drives the mower deck.) The mower deck must be removed. Bret
the main thing is that your belt that goes from the deck to the pulley beneath the pulley on the engine that makes the mower move there is a pulley below that and the belt is to tight. that is the only thing i can think of. hope this helps
The deck must be slipped beneath the machine from the left, the lift lever locked down and the rear hangers and front hanger plate attached. The belt will take take a 90 degree twist with the front part to the left side.
You can change the drive belt, on your lawnmower, by loosening the tensioner pulley. With the tensioner pulley, loosen the drive belt will come off and can be replaced.
One might learn how to install a 42 inch deck belt on a John Deere lawnmower by looking at their user manual. A better route to this may be to take it to a lawn mower shop for repair.
on the mower deck
Answer No, it won't go faster, but it may accelerate more quickly. Problem with removing the mower deck is if you pull out in a higher gear you'll run the risk of wheelie-ing backwards onto yourself... hurting you and the tractor. If you need to go faster, the easy way is to replace the drive pulley on the engine with a larger diameter pulley. You may need to buy a longer belt to accommodate the larger pulley.