Replacing a tub faucet involves removing the old faucet from the tub, replacing the old spout nipple with a new one and attaching a new faucet on the new nipple. Obtain a new faucet of the same style and size as the old one before attempting this task. On top of the new faucet, you need a screwdriver, Teflon tape, caulk, a new spout nipple and a pipe wrench.
To remove the old faucet, locate the faucet's set screw, and loosen the screw with the screwdriver before pulling the faucet off the spout nipple. For a faucet without the set screw, remove it by inserting the screwdriver into the faucet's open end and rotating the faucet counterclockwise to break it before unscrewing it off the nipple with a hand. To remove the old spout nipple, locate the bonnet nut, which is typically located at the spout's base, and loosen it with the pipe wrench. Once the nipple is off, place the new nipple over the nipple threads, and secure it in place with the tape before replacing the nut.
To fix the new faucet on the spout nipple, first tape the nipple spout thread, and screw the faucet over the nipple, taking care not to over-tighten the faucet to avoid damaging the nipple. Finally, replace the set screw, and seal any gap between the faucet and the wall by caulking.