Toilets, Sinks, Showers, Tubs and Disposals - removal of stem from single handle bath/shower

how do you remove the stem from a single handle shower

control handle

Typically:

Step 1: turn off the water supply to the house.
2: remove the cover plate from the handle (either plastic or metal that is usually pried off)
3. Pull off handle
4. Here's the fun part - determine what you need to unscrew - depending on type/model/brand - to remove the cartridge.... and do so (or post back with the new "issue" at hand).
5. unscrew cartridge holder assembly - and simply pull out the cartridge to repair/replace.

Typically - simple deductive reasoning will get you through the process....

Welcome to the forums! Not knowing what brand you have, I'll give a generic description until you fill us in. If it is a Delta, the plastic cap comes off, the phillips head screw is undone and the handle pulled off. With the water off, and using a Delta spanning tool, release the nylon spanner nut, then undo the collar. Delta doesn't have a "cartridge", but rather two washers and springs to be replaced, as well as the ball and cap washer, which can be purchased as a kit. Moen, you pop the cap, undo the screw, pull the handle, note there is a horseshoe looking clip installed from the top of the shaft. Pry it out and with a pair of pliers, pull on the cartridge (water off). Take it with you to the supply house for an exact, and I mean exact replacement.