Open the top of the nanocube and you'll see the return line on the far right, if you grab the elbow and wiggle it while pulling back it will come out. After the elbow is loose just pull the pump and all straight up and out of the tank.You can then pull the hose off of the pump and slip it on the new pump and put it back by reversing the procrdures. Run the pump on it highest setting and it'll be fine.