Without a manufacturer's name and model number of the engine, it is impossible to determine the details that you are inquiring about. There are too many variables.
To change the oil, locate the drain plug if your engine has one. It will probably be a square drive plug.
Many engines have no such drain plug. In this case, the simplest method to drain the engine oil is to pour it out of the port where it is added to the engine.
To tilt a 4-cycle over to accomplish this, always keep either the air filter or the spark plug pointed upward. The oil will then pour out from where it goes in. Never turn the engine where the spark plug or air filter is pointing downward.
Refill the engine with enough oil to reach the full mark on the dipstick. This amount varies with the engine's application. Be sure that the engine is level when checking the oil fill.
There is no standardized measure of the horsepower of an engine. Power ratings on small gasoline engines vary greatly from one manufacturer to another.
Thank you for asking,