If you mean shower valve, screws are for shower valve coverplate.
By replacing the entire shower body
Behind shower valve handle and trim plate
A leaking shower valve by installing a new cartridge.
changing a shower valve can be sometimes impossible with out cutting a hole in the wall behind it. If you have a shower valve that is leaking through the valve and out of the shower head when shut off then I recommend trying to find new cartridges or replacement seals for the valve. If you need to replace the shower valve then I would cut a hole in the sheet rock behind the shower valve big enough so you have enough room to replace it. Sometimes if you can't get behind the shower wall and your water pipe isn't galvanized then it might be possible to change the valve through inside the shower but it can be a real struggle and most of the time you will need a wider trim plate. If you don't have much experience in soldering or using pex pipe and fittings then I would save you a headache and call a service plumber.
Yes, remove your old shower valve and fit a new Moen anti-scald valve. This will not change when other items are turned on.
Standard height for ADA (handicap) is 42 " center of valve to shower floor.
Cut out the drywall in the wall behind the shower. Replace the valve. Patch the drywall.
Shower may have an anti-scald shower valve installed. If so, shower valve can be adjusted to desired temperature.
Your water pressure is low. Consequently, when cold water is diverted to another application such as a toilet or a sink, the amount of cold water available at the shower mixing valve decreases as the low pressure is unable to keep up with the shower's demand. This causes a hotter mixture at the shower head. The solution is to either improve the cold water supply to the shower or to replace the shower control valve with a temperature compensating type. Pressure balancing is the cheapest and simply changes the shower temperature according to the pressure in the cold and hot water lines. When the toilet or sink is used, reduced pressure to the shower valve is detected and the valve reduces the hot water pressure, thereby maintaining the temperature. The more sophisticated approach is a thermostatic shower control valve. These are significantly more expensive, but will not reduce the pressure at the shower head (a drawback of the pressure balancing valve). The thermostatic valve would be required when one shower control valve is operating several shower heads. Moen, Kohler and Delta all make both types of control valves. They can be readily obtained from a local plumbing supply house.
A trim kit is just the outside parts that you see. This will make you faucet look better, but it wont affect the function of your old valve. If your shower valve doesn't work right, replace it.
The valve is not be diverting all the water. This valve may need to be replaced.
Some shower valves have integral stops which can be accessed by removing the trim plate. Most shower valves don't have these and the water is shut off by turning off the main valve to the house or apartment.
Though not a plumber, I can say that shower valves are usually made of brass(a very good material). Therefore they are also expensive to replace (50 dollars for the valve, 150 dollars per shower valve if done by a competent plumber). Therefore, when you notice a leak coming from your shower, try to replace the seat washer (usually the hot water side needs to be replaced first). If you still have a leak, it's time to replace the shower valve.
42 to 48"
The valve in the shower control needs to be renewed.
Replace the shower valve.
The same height as the normal western shower valves, this is why they are yellow, they can't show because they can't reach the valve.
mixing valve in a faucet: ok I will assume you are refering to a shower valve, that is the only faucet w/a mixing valve: shut off the hot and cold water. cut out valve or unsweat it. clean and flux new valve, pipe and fittings(if used) sweat in new valve
no, you can buy a new shower head and install it. but if you want to change the controls you will probly have to buy a new unit. Unless you can cross reference the parts to see if they will fit. and you might be able to change the handle or know without changing the controls
try replacing o ring on spindle
The incoming hot and cold lines go to separate inlets on the mixing valve. The single output will go to both the spigot and the shower head.
Seats in the main valve body are leaking by, allowing water to go to the shower head.
depending on your spout diverter if its a valve or is it on the spout it self, if the diverter is on the spout then your diverter is not letting full flow of water out of the spout and its putting enough pressure to allow the water out of the shower head, I had this problem before and if you change the spout it should fix the problem. If you have a 3 way valve which is on the wall then i would suggest replaceing the parts in that valve if possible other wise change out the divert valve. If your broke like me and want a cheap fix then put either a water flow resistor or a shutoff right before your shower head.