Here are the steps to change the oil in your Ryobi 650R lawn mower:
1. Place the lawn mower on a level surface.
2. Turn the fuel valve to the "Off" position.
3. Disconnect the spark plug wire from the spark plug.
4. Remove the oil drain plug from the bottom of the engine and allow the oil to drain into a suitable container.
5. Replace the oil drain plug.
6. Remove the oil fill cap and add the specified amount of SAE 30 weight oil.
7. Replace the oil fill cap.
8. Reconnect the spark plug wire to the spark plug.
9. Turn the fuel valve to the "On" position.
10. Start the lawn mower and let it run for a few minutes to circulate the new oil.