Mixing valves are something of a mixed blessing. Also known as anti-scald valves, these devices help keep you safe in the tub or shower by preventing the water flow from becoming hot enough to scald you should the cold water pressure drop suddenly. The down side is that on occasion you can't seem to get the water hot enough for a decent shower. This is usually due to changes in the available hot water supply, or to an overprotective valve setting. A minor adjustment might be all that is needed to get you back into pleasantly hot water.
Loosen the set screw located on the underside of the shower valve handle. Use the wrench provided with the shower valve or an Allen wrench of the proper size. Pull the handle off of the stem and set it aside.
Unscrew the trim sleeve, being careful not to lose the O-ring seal that seals it to the trim flange. Remove the flange. Set both items aside.
Pull the mixing valve adjustment gear out of the valve so the stem is free to turn fully counterclockwise. Turn the stem until the desired maximum water temperature is reached. Replace the adjustment gear so that the stem cannot turn beyond the maximum set temperature.
Install the trim flange and hold it in position while screwing on the trim sleeve. Make sure the O-ring stays in position on the sleeve. Place the handle on the stem and tighten the set screw.
Check the valve for proper operation.