To change the oil of a Husqvarna Norden 901, follow these steps. Make sure the engine is warm but not too hot. First, place the motorcycle on a flat and solid surface. Find the oil fill cap, usually located on the left side of the engine. Remove the cap to allow the old oil to drain more easily. Then, locate the oil drain plug on the engine case. Place a collection container under the drain plug and unscrew the plug with a suitable wrench. Once unscrewed, let the used oil drain completely into the collection container. When the oil is completely drained, unscrew and remove the oil filter with an oil filter wrench. Make sure to clean the filter mounting surface thoroughly. Take a new oil filter and apply a thin layer of new oil on the gasket before installing it. Screw the oil drain plug back in and tighten it securely. Fill the engine with new oil through the oil fill cap hole, using the oil recommended by the manufacturer and following the specified capacity in the owner's manual. Make sure not to overfill the engine and check the oil level with the oil dipstick. Finally, reinstall the oil fill cap, start the engine for a few minutes, and check for leaks. Once confirmed that there are no leaks and the oil level is correct, the oil change is complete.