I assume you mean the oil in the lower unit gearbox. I do recall that engine to be 2 stroke and you don't need to change the engine operating oil as it changes itself as it is consumed and you refill the tank(s).
Engine vertical, remove the drain plug located below the gearbox bulge. For a reference point, check condition of oil. If it hasn't been changed for awhile, it will be almost black. If recently, blue/black...color of the Quicksilver high perf. gear box oil. If any other color you have water ingestion and have a leak somewhere.
Up along the horizontal fins, close to where the LU and mid sections separate, will be one or two (vent) screws just like drain screw. Remove them and let the unit drain.
Using the quart Quicksilver high perf. oil (WW has it in sporting goods) with the hose, pump and screw in adapter, fill the LU until oil starts to come out the drain plug(s)....it will have bubbles and I usually let a little run out till I start to get close to solid oil.
If only one vent plug, without changing anything else, install and tighten the drain plug.....large blade screwdriver good and hand tight. If two plugs, do the forward one then keep pumping till the rear one does the same thing and cap it.
For ease of assy, you may want to tilt the engine up for this step:
With the drain screw ready (with new seal) remove the fill adapter and install and tighten the drain plug. You will loose a small amount of oil but that is to be expected; just try to minimize what you loose.
That's it.
