Stuck Screw Stops on Shower

[HandyDDad]

I need to replace the cartridge on my Kohler shower. I am trying to turn the screw stops to shut the water off at the shower but they are stuck. I have tried with about 80% force in either direction but they will not budge. Should I try turning the screw with greater force? Can I break something? Which direction should I turn them and how much to shut off the water? Shower was installed about 10 years ago and I don't think screw stops have been turned since then. Images below. Thanks.

 

[Geofd]

My 1st advice ise to use a flat head screwdriver with squared off edges on the shaft use a bigger screwdriver than the size of the stops, I usually put the screwdriver on the stops and give them a good whack then use an adjustable wrench on the shaft and your body weight to turn the stop, usually Kohler will have replacement stops if you have to change them out

 

[HandyDDad]

My 1st advice ise to use a flat head screwdriver with squared off edges on the shaft use a bigger screwdriver than the size of the stops, I usually put the screwdriver on the stops and give them a good whack then use an adjustable wrench on the shaft and your body weight to turn the stop, usually Kohler will have replacement stops if you have to change them out

I assume I should turn them to the left? Do they require a full rotation to shut the valve or 1/4, 1/2? Thx.

 

[Geofd]

Clockwise ki would think,until it stops