A hot tub shoots water under pressure through jets on the tub's inside. The people in the tub regulate the temperature of the water through two faucet handles, operating like a bathtub's. You can change a faucet on a hot tub in much the same manner as a bathtub's faucet, with some minor differences. You will need household tools that are commonplace to the home and a replacement faucet handle from a home and garden shop or a pool/spa supply store.
Trip the circuit breaker in the fuse box that supplies the hot tub with electrical power. Turn the power switch on the tub to "Off" if it is not already set so.
Open the side panel at the bottom side of the tub -- in some cases screws will need to be removed first using a Phillips screwdriver. Turn the water valves inside clockwise until you feel resistance.
Insert the tip of a flathead screwdriver beneath a corner of the cap at the top of the faucet. Lift up on the tip to loosen the cap. Pull the cap off and place it aside.
Remove the screw from inside the top of the faucet handle with a Phillips screwdriver. Place the screw aside for use with the replacement faucet handle.
Grip the faucet handle, just beneath the hole at the top, with a pair of pliers held in one hand. Strike the side of the pliers that is farthest from you with a hammer held in the other hand. Repeat this procedure until the faucet begins to turn counterclockwise. Remove the pliers.
Unscrew the handle. Pull the handle off the rod it is seated on. Place the handle aside. Unscrew the plastic tube that is over the rod using your fingers; if the tube will not cooperate, loosen it first by twisting it counterclockwise using a pliers.
Remove the tube from the rod. Clean the rod with a dry cloth. Clean the base of the rod with a dry cloth.
Place the replacement faucet handle's plastic tube over the rod; if the tube is threaded, screw the tube onto the rod with a clockwise motion.
Screw the replacement faucet handle onto the rod. Tighten the handle with a pliers -- place a hand towel around the faucet handle to keep the jaws of the pliers from scratching.
Insert the screw that you removed earlier into the top of the replacement faucet handle. Screw in with the Phillips screwdriver. Place the cap that coms with the replacement faucet handle on the top of the handle. Press down on the cap to secure it to the top of the handle.
Rotate the valves counterclockwise to restore the flow of water to the tub. Place the side panel back on and, if necessary, reattach the screws. Restore the electric power at the fuse box.