To change the oil in an ATV, start the engine and let it run for a few minutes to warm up the system. Turn off the engine, remove necessary panels to access the oil filter, and clean the area around the dipstick. Place an oil pan under the ATV, remove the drain plug to let out the old oil, and then remove the oil filter. Replace the drain plug, install a new oil filter, and pour in the new oil. Start the engine and let it run for a few minutes to circulate the new oil.