The most common thing that could happen is the deterioration of internal springs and seats that could lead to leaky faucet. A replacement cartridge is necessary along with a couple of hand tools and assembly kit should help you get the job done. Here are some steps that you can follow.
1. Turn Off Water Supply
Take note of the connections going through that faucet you have in your shower. For some, there are access panels that have isolated shut-off valves found in the bathroom. Others can be located in adjacent rooms or hallways or closets.
After determining where to find the valve, you need to rotate it clockwise so that you can stop the water flowing from the valve. If you have no isolated shut-off valves at home, then you just have to turn off the main connection. After closing the main water supply valve, you have to release the pressure and excess water by opening the faucet.
2. Remove Faucet Handle
Use a screwdriver to remove the faucet handle button. For the handle set screw, use Allen wrench that should be appropriately-sized or a Phillips screwdriver for some models. You can now fully remove the faucet handle and put it aside. After removing the faucet, try to remove the sleeve outside and unscrew the brass-like bonnet.
3. Cartridge Position and Installation
Try to notice the position of the cartridge labeled Hot Side by grabbing the brass valve stem using a pair of pliers and pull the cartridge outside.
Take the new cartridge with the Hot Side indication on top of the cap using the same position noted when the old cartridge was removed. Make sure that the new cartridge should be seated exactly with tabs atop the white cap. This should be fully engaged with notches along the brass body.
If possible, change the bonnet and tighten it using your bare hands. You should also substitute the outside sleeve with a new one.
4. Rotation Limit Stop
Check the position of the rotation limit stop that should go with the new cartridge. This is the positioning notches and adjustable lever found on top of the cartridge. Make sure that the new one will be in the same position as the replaced item.
5. Replace the Handle
You can now replace the handle button and handle it after doing the initial installation. Check if the handle is set up properly by opening it fully. Thus, you can now turn back the water supply on to allow the water and air to clear out the new installation. At this point, you should be able to check if there are leaks. Likewise, you can now check if your water temperature control is working fine.