Hello!
How do I remove the stem of Stanayne Single Handle shower?

Shut water off
Remove handle and face plate
Remove the chrome sleeve
Remove the copper cartridge clip
Give good PULL on stem or reattach handle and then give good pull to remove cartridge.
Then, pulse water on/off to clear valve of any sediment
Then replace with a new cartridge.
Replace clip
Replace sleeve
Replace knob
Turn water back on.
TEST