In order to remove the escutcheon, (the big round plate with the screws in it) It may be caulked to the wall. You first remove the handle and unscrew the round cover that is over the valve body, this will give you access to the adjustments for limits stops that control the temperature mixing. Or the ability to remove the cartridge and replace it.
For removing the handle,there will be a set screw on the handle some were that you will have to loosen so you can pull the handle off, I am betting it is on the under side (bottom) of the handle but i have seen them under the little blue and red symbol. You then need to follow the manufacturers instruction to set the temp limits.
It usually involves pulling out (slightly) a round plastic disc that is keyed in to another round plastic part, then turning it one or several key slots and sliding it back in. This changes how far the handle can be turned to the hot position.