Often when taking a shower, you will desire a bit more hot water pressure. However, because the hot water doesn't have a separate pump, in order to adjust the pressure of the hot water, you must increase the pressure in the entire system.
Monitor the pressure gauge near the pressure switch; note the turn on and turn off pressure. In a typical system, the turn on pressure might be 20 psi, and the turn off pressure, 40 psi.
Decide on a new higher range for your pressure. The typical high pressure is 30 psi to turn on and 50 psi to turn off. You don't want to increase the pressure too high, or it might burst things like the bladder inside the pressure tank or even pipe seams.
Turn off the electricity to the pump and drain the water. The pressure gauge should read zero, and the water should stop.
Check the air pressure in the pressure tank using the tire pressure gauge.
Increase the air pressure to 2 psi below the desired turn on pressure using your air compressor.
Remove the cover from the switch. There should be a nut on the top that holds the cover on. Loosen the nut and pull the cover off.
Tighten the nut on the larger spring. Using your wrench, turn the nut clockwise (down). Each full turn should increase the pressure about 4 or 5 psi, so 10 psi would be two or two and one half turns tighter.
Test your pressure. Turn the power back on and turn the water on and off. Note the pressure that it turns on and off compared to your desired pressure. Tighten or loosen the large spring as necessary to correct the cut-on pressure.
Set the differential if necessary. Normally, the differential between the cut on and cut off pressure should stay at 20 psi. If you want a larger range between the on and off, you can tighten down the smaller spring. Conversely, loosening the smaller spring will decrease the difference between the cut-on and cut-off pressure. Some people mistakenly believe the small spring regulates the cut-off pressure, but unfortunately this is not true -- it is the differential range between the cut-on and cut-off.
Test the cut-on and cut-off pressures again by opening a faucet with the electrical power turned on while watching the pressure gauge.
If you are relying on city water, the only way to increase your hot water tank pressure would be to add a pump and storage tank because the pressure is regulated by the city for all residents. An individual pump would allow you to increase the pressure within your house by storing extra water.
Be careful when dealing with water and electricity in close proximity. There is always a danger of fatal electric shock. Most home systems are not designed to stand pressures above 65 psi.