To replace a bathtub spout you will need only a small handful of tools. First and foremost, make sure that you have a good screwdriver (or allen wrench.) On the bottom of the existing spout, there should be a setscrew on the underside of the spout, close to the wall. Some bathtub spouts have the ability to twist in order to make access to this screw easier. If your spout doesn’t twist easily, it would be best to simply remove the screw from its current position instead of damaging the fixture by forcing it.
One of the biggest reasons why bathtub spouts are damaged is from women shaving their legs. The bathtub spout makes for a convenient footrest; however, the spout is in no way designed to support any weight or force exerted against it. Over time, this can damage the diverter, loosen pipe connections or worse.
If you suspect that your diverter or pipe connections have been damaged, call a professional plumber to check it out and repair any damage before replacing the bathtub spout.
Once the screw is removed, twist the bathtub spout counter clockwise. Placing your screwdriver inside the spout should give you better leverage as you twist off the spout. Once you have completely removed the spout, use a chisel or razor blade to remove any remaining caulk. It is a good idea to take your old spout with you to the hardware store to ensure that you purchase the proper sized replacement spout.
With the new spout in hand; twist it clockwise until it fully covers the pipe and is fully in place. Use your screwdriver to tighten the setscrew. Finally, run a bead of caulk a quarter inch thick around the outside of the spout where it meets the wall. Wipe away the excess caulk and let it dry before you use the spout.