Park the golf cart on flat, stable ground. Apply the parking brake.
Place wheel chocks in front of and behind the front wheels.
Use a jack to lift the rear of the golf cart. Secure the rear end with jack stands.
Place a pan under the differential. Remove the check/fill plug with a ratchet and socket.
Place the inlet hose for the siphon pump into the fill hole in the differential. Place the outlet hose into a container. Pump the siphon to remove the differential oil.
Insert a funnel into the differential's fill hole. Pour in differential oil until the level is just below the bolt threads. Replace and tighten the bolt.