How Do I Remove This Shower Handle?

Total newbie here. I want to replace the shower handle on my kids' shower. I can't figure out how to take off the existing shower handle. I think I am supposed to use an allen wrench on this part here, but that isn't working.



Here are pictures of the handle.







Am I just doing it wrong? If it is stripped, how would I remove it? Should I just give up and call a plumber?

I did this once before with a different shower and was successful. I think once this is off, I will be good to go, I just can't figure out how to remove it. Thanks for your help!

yes. Unscrew the allen screw. If it's stripped then drill it out.

Looks like a Valley valve.

this is the cartridge and you have to replace the cups and springs if you want to rework the working parts.

Be Forewarned. Sometimes the chrome cap nut is tricky to remove with out damaging the valve body.
I believed just behind the cap are 3 small copper tubes.
If you try to unscrew the cap you can twist those tubes and damage the valve.
Trick is to use a pipe wrench on the cap. DO NOT try to torque it off.
Set the pipe wrench and then tap it with a hammer. The jolt/impact will break it free.
You can get a new. wipe the threads with a little stem lube before you reinstall it.

You can replace the handle with an acrylic one if you prefer.

Thanks so much Mr_David. I sprayed a whole lot of WD40 on it and got it out. The pictures you posted were extremely helpful. Thanks again!