Russ I don't know if you got all the manuals with the machine but if not you can download them from the manufacturers website. Thats Roots, Hypro and Honda.
If you are changing the blower oil then you need to undo the lower plug which is right on the bottom. This will drain off the oil, also open the top vent and filler obviously.
The fill level is the lower of the 2 plugs on the side, the one on the right as you look from the back. So you drain, put the bottom plug back in, remove the lower side plug and fill with oil until it runs out of the side hole. Put the side plug back in and pull the starter cord a few times then check the level again and is needed top up until it runs out of the side hole again. Thats it.