Shower Control Knob Stuck

I was trying to take off the shower control knob, the one which diverts the water from the tub to the shower head. I have got the screw out, but the know is stuck and will not come off. Any suggestions?
Thanks and have a great day.
John

If you are speaking of a tub spout diverter, replace the entire tub spout as the assembly normally doesn't have repair parts. This will also solve your issue of water coming out of the faucet the same time as the shower is running.