Shut off the pool pump and disconnect it from the electric source. Most pool pumps are scheduled to run by timer; disconnect the pump from the electric source to prevent it from turning on while you're in the middle of cleaning the impeller.
Turn the hose valves to the "Off" position. If you have on/off valves installed on each pool hose, make sure to turn them off to prevent the flow of water to the pump. If you don't have on/off valves installed, disconnect the pool the hose from the pool pump and insert the open end in the pool to keep the water contained.
Open the pump basket lid and remove the pump basket. The water currently in the pool pump will begin to flow out, but that's okay. While you're in the pump basket area, clean out the debris in the basket.
Reach beyond the pump basket through the tube to the impeller. Remove any debris you find in the connecting tube. After clearing the tube, reach a little further toward the impeller compartment area. Feel for dirt, leaves or debris. If there is no dirt or debris, then you impeller cleaning job is complete. However, if there is difficult-to-remove dirt, then you still have a little more cleaning to do.
Detach the pool pump from the pool filter. This will give you access to the impeller from yet another angle. You can reach the impeller through the tube connecting the pool pump to the pool filter. Reach in to pull the debris lodged in the impeller. If you can't get it here, it's time to dismantle the pool pump.
Open the pool pump to access the impeller. On some models, such as Hayward pool pumps, this involves loosening several bolts to access the impeller. Refer to your manufacturer's instruction manual on how to dismantle the filter. The impeller is in the housing right behind the pump basket assembly. Once you've disconnected the assembly. The impeller is in full view and easy to clean.