I assume this is an inboard motor or you would not be asking this question. The engine must be lifted from the boat, not as hard as it sounds. The engine mounts, prop-shaft, and fuel line must be dis-connected.
For the next bit you will require 4 hefty lads or a block & tackle. I recommend the latter, nowhere near as noisy or thirsty. Lift your motor and drag out the boat and trailer.
Rig a temp. Fuel supply and run the engine to heat the oil. Put in new filter and oil and re-assemble It is many years since I worked on them but I do not think it has changed.
You do not hear of car engines in boats these days, but in the sixties we loved the V8s for water ski-ing. Being towed behind one of those full bore was a buzz.
I have an Oil Boy pump that I used with marginal results. First of all my engine is a 5.0 Mercruiser. I have the boat in the water so I thoroughly warmed up the engine so the oil would be hot.
After that, I punctured the top of the oil filter to allow it to drain into the pan as much as possible. This also makes less of a mess when you remove the filter (which is what I did next). The Oil Boy pump has the "Garden Hose" adapter which screws on the top of the Mercruiser dipstick so I used that.
After several pumps to start the flow everything went fine. I waited until the pump started sucking air before I stopped.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.