There is a few different ways to change the oil. You can drain it into the bilge and clean up after you're done. You can also buy a pump to suck it out from the dip stick tube. The other method I know of requires the boat to be equipped with a hose screwed into the drain on the pan.
As far as oil goes you can use straight 30 weight or the Merc 20w 40.
The motor does have an oil filter. If youre facing the front of the engine the filter is on the right (port) side of the engine bottom corner furthest away from you.
This make me really nervous - There is not alot to an oil change, but if you are not comfortable with the task, it may be best to pay a pro.
As for removal of the old oil - the pump out through the dipstick is the best method. It is neat, clean and doesn't take all day like the tube from the drain plug. I have a vacuum oil extractor that I purchased from Northern tool for $40 - it works great. Hook up the tube, pump it up, open the valve, sit back and wait till it finishes.
