Hi- I am trying to figure out how to remove the shower faucet (to turn water on and off) and having no luck. Can anyone help?

Hi- i am trying to figure out how to remove the shower faucet (to turn water on and off) and having no luck. Can anyone help?
Do you wish to replace the valve? Turn the water off to it? Or change a cartridge? What's the brand nain of the faucet? One handle or two knobs? How old? Please give us more details. Thanks, Tom