Use the user's manual to locate the pressure relief valve, which should have a plastic tag around it stating the ideal operating pressure range of your boiler.
Check the boiler pressure gauge on your boiler and compare the reading to the operating pressure on the relief valve tag. If your boiler's current pressure is within the normal range, it may be better not to adjust it. If the pressure is not in range, continue to the next step.
Locate the fill valve to raise the pressure. Open the valve and watch the boiler pressure gauge as the pressure rises. Close the valve once the pressure has reached the desired level.
Locate the boiler drain to lower the pressure. Open the drain and watch the boiler pressure gauge as the pressure falls. Close the drain once the pressure has reached the desired level.
Run your boiler through a complete cycle to ensure it works properly after changing the pressure. Thoroughly check all the pipes and valves in your boiler system for leaks.