how can i increase pressure and stop leak on my baxi combi boiler?

i have hot water and hot radiators but hot water takes time to heat up and radiators not hot enough especially upstairs. there is slow dripping leak from inside boiler just behind control panel on right hand side. pressure is low very low at 0 almost. i dont know the model number of the boiler all i know it is about 4years old and a baxi make nothing special.