I need to find out how to set the presser on/off control craftsman multistage jet pump model number 390.253251?

Remove the plastic cover on the pressure switch and you should see 2 bolts with springs and nuts on them. The bigger one adjusts both cut in and cut off pressures. Usually 20psi difference. The Small one changes that differential. U need only tighten down the big nut to increase pressure. With the hydro to the pump off tighten down the big nut a few turns then turn hydro on and run some water till the pump turns on. Continue this procedure till desired pressure is reached.