how do you change the oil in a lawn mower?

It depends which make it is really, but the principle is the same.... some machines have a drain plug at the lowest part of the engine that you unscrew to let the oil drain out, but usually its easier to tip the machine onto its side and let the oil drain out of the filler/dipstick plug hole into a suitable container. You then refill the machine with the correct grade of oil (usually SAE 30) until the level is exactly right on the dipstick or level plug.

John
July 2009