how can i fix the brakes and adjust the parking brake of my JCB 3X 2003?

the brakes of my JCB 3X Contractor 2003 are very weak even after i have allready changed the two main pumps and check the rear diffrinsion from inside and the braks were good un it. when i step on the brake pedal it goes very down and the result is very weak specialy on a slope surface, please i need so suddestions.
the parkind brake is very weak and it needs to be adjusted but i don't know how to do it.