Changing oil in your outboard motor is much like changing the oil in your car. First you will want to locate the gearcase and loosen the top screw. Next place a drain pan beneath the unit to collect the used oil. Loosen the bottom drain screw and remove it. Let the oil drain for about five minutes, longer if it is slow to drain. Check your oil for metal particles, or if other liquids like water are present. Should either be present, consult a mechanic or qualified service individual.
When the oil is done draining, using mercury oil or your brand of choice, fill the unit from bottom to top, until oil comes out the top screw hole. Screw the top screw in first, and immediately replace the bottom screw. Ensure both screws are tight to prevent leaks.