In general, a relief valve is set by turning a screw, or adding shims.
To raise pressure, a thicker shim is required, and if screw type, tighten the screw more will increase pressure relief.
You should know the max pump pressure and valve rated pressure.
Have a hyd test set available, and plug in to one of the QD's, and push the lever to pressurize the QD/gage momentarily.
Some people adjust the pressure to about 50 to 100 psi below the pumps max pressure.
This increase in pressure may allow you to lift a greater load, and you might need some more ballast on the back.