How do you empty the oil on the Briggs and stratton 4.5 hp lawnmower to refill it?

there should be a drain plug under the mower where the blades are. to fill it is on the top where you check the oil.

there is a drain plug under the mower where the blade is. to fill it is where you chech your oil.

Many mowers do not have a drain plug, simply remove the dipstick and tip the mower on its side and dump it out the filler tube into a proper container.