How to adjust a water pump pressure switch/regulator?

You probably have a switch with two nuts, one large and one small. Turning the large one clockwise will increase both the cut in and cut out pressures. Turning it CCW will decrease both pressures. Do this with the power off. Don't be timid. Begin with a full turn, then turn the power back on and see what you have. Keep at it until you get what you want.

Speedball found this really nice link. I copied it from one of his previous posts. http://www.sta-rite.com/resources/images/13433.pdf

Which nut adjusts water pump cut on or cut off?
The larger nut in the pump pressure switch: Usually the larger nut in the pump pressure control switch adjusts the pump cut-on ("cut-in") AND pump cut-off pressures simultaneously. That means that whatever the gap is between the cut-on pressure and the cut-off pressure, that gap is maintained, but the entire operating range of the pump is raised or lowered. Turning the large nut clockwise RAISES BOTH the cut-on and cut-off pressures. So turning the large nut clockwise shifts the whole operating pressure range of the pump UP to HIGHER pressures.
Conversely, turning the large nut counter-clockwise will lower the whole pump operating range. This is the simplest adjustment to make.
The small nut in the pump pressure switch: this nut is used to narrow or widen the gap between the pump cut-on and pump cut-off pressures. Turning the small nut clockwise (tighter) will RAISE the CUT-OFF pressure, and vice versa, loosening or turning the nut counter-clockwise will lower the cut-off pressure. Watch out! If you loosen this nut too much you can set the cut-off pressure below the cut-on pressure and the pump will turn on and run forever (or until it burns up.)
Which nut to turn in the pump pressure switch control, and which direction to turn it, are usually visible on a label inside the pressure switch cover. Above we show photos of a common Square D water pump pressure control switch and the label with pump control adjustment details
Good luck Tom