If your shower is spitting water from the tub spout instead of flowing through the shower head, or the diverter handle makes a grinding noise or won't turn, or if the hot water is suddenly gone, your diverter valve and cartridge should be removed and replaced. Diagnosing the problem and removing the shower diverter is an easy undertaking that even a novice do-it-yourselfer can do. The only tools you need are a screwdriver, an Allen wrench, and replacement parts.
Before removing any parts, cover the drain with a rag or towel. Turn off the main water supply to the shower. Turn the faucet on to release the pressure and drain the water in the water lines.
Remove the diverter handle. Acrylic handles have a decorative button covering the handle screw. Use a screwdriver to carefully pry off the button without damaging it. Remove the screw and lift the handle off. Note that some types of buttons screw on and are removed using a wrench. Faucets with no button on the handle have a screw on the underside. Use an Allen wrench to remove the screw then remove the handle. Some faucets handles have washers and adaptors that just slide off.
Use a screwdriver to unscrew the screws on the escutcheon (decorative metal plate on the shower wall) then lift the escutcheon off the wall. If the escutcheon is caulked use a razor knife to slice the caulking. For escutcheons with no visible screws, unscrew the threaded sleeve by hand then lift the escutcheon off the wall.
Unscrew the metal gasket or flange that holds the valve assembly in place using a screwdriver. Pull the valve assembly straight out. Use a towel to wipe up escaping water to keep it from dripping down the inside of the wall. Locate the cartridge (look for two water chambers side by side) directly behind the valve assembly and pull it out.
If you are fixing a leak, the problem can be just or worn valve assembly or it can be a worn water cartridge. You can replace the valve assembly and test the faucet to see if the problem is solved or you can do the same with just the cartridge. However, you should replace both parts at the same time. Use a toothbrush to clean old parts that you plan to reuse.
There are many different manufacturers, models and styles of diverter faucets. Allow for slight differences in internal parts.