How do you change the oil on a 3 hp mercury outbourd?

To change the oil on a 3 HP Mercury outboard, first ensure the engine is turned off and cool. Remove the oil drain plug, typically located at the bottom of the gear case, and allow the old oil to fully drain into a suitable container. Replace the drain plug, then use a pump to add new oil through the fill hole until it reaches the appropriate level, checking with the dipstick if available. Finally, securely replace the fill cap and dispose of the old oil properly.