Normally near the base of the boiler there is a steel braided pipe which feed the boiler with cold water to pressurise the system. This will have a small 90 degree tap on it (bit like a washing machine tap)
Close by there should be a small pressure gauge. By opening the tap very slowly you should see the needle on the gauge go up when it reaches 1.5bar turn the tap off.
If you exceed the pressure it can be reduced by bleeding any of the radiators. Hence this also means that if you bleed radiators you will need to reset system pressure.
If you are still not certain then ask the person who installed the system to help.
M
December 2010