Certain style pumps cannot have the oil changed or added. These are sealed pumps and will normally be labeled as "Axial Cam" style pumps. "Triplex Plunger" style pumps can have oil added and/or changed. If you have this type of pump, there will be a fill port on top of the pump that unscrews. You will also have a threaded plug on the bottom of the pump so that you can drain the old used oil.