To change the oil of a Ducati Monster 900, start by making sure the motorcycle is parked on a flat and stable surface. Start the engine and let it run for a few minutes to warm up the oil, making it more fluid and easier to drain. Turn off the engine and place a collection tray under the oil drain plug, located on the bottom of the engine. Use an appropriate wrench to remove the drain plug and let all the old oil drain out completely. Once all the oil has drained, reinstall the drain plug and make sure it is securely tightened. Now, locate the oil fill plug, usually located on the side of the engine, and remove it. Use a clean funnel to pour the specified amount of new oil recommended by the owner's manual. After adding the oil, replace the fill plug and start the engine for a few minutes to circulate the new oil in the system. Turn off the engine and check for any leaks around the drain plug and fill plug. Check the oil level again after a few minutes and add more oil if needed to reach the correct level. Finally, dispose of the used oil properly by taking it to an authorized collection center. This procedure ensures that the engine of your Ducati Monster 900 operates efficiently with fresh and clean oil, contributing to the longevity and performance of the motorcycle.