If the system is under pressure, please call in a professional. Pressurized hydraulic fluid can be deadly!
If not under pressure, then normally you just loosen the nut at the end of the hose, and put a catch pan under it to collect the fluid remaining in the hose. At least one end of the hose should have a swivel nut that can be turned without turning the hose with it.
If you check the wrench size of the nut first, you can get the proper size caps and plugs to put on the fittings ( 2 on hose, 2 on the equipment ). This will help keep the mess to a minium while you take the hose to the hydraulic shop and have them make a new one.
If this doesn't seem to explain your problem, please post some pictures. There are many styles of hydraulic fittings, and these general instructions may not apply to your case.
Rick