How do i repressurise a Worcester 240 BF boiler?

Hi,

We recently moved to a new property and inherited an old boiler (about 15 years old). It works fine, however the pressure on the dial reads just above 0 (should be 1.5). Can someone tell me how to increase the pressure please? It doesnt appear to have any sort of place to insert a key to increase the pressure.

This is the instruction manual for my boiler:

http://www.unipol.org.uk/Housing/About_your_tenancy/applianceguides/centralheating/Worcester%20240.pdf

Any help much appreciated!

Thanks,
Jack