Is it a single speed? If it is, there should be a bolt underneath the engine, just in front of the stand. That's the drain plug. Take it out and put an empty can under it to catch the used fluid. On the right side of the engine there's a fill plug. It's larger than the bolts that go around the side cover. Take that out and put the drain plug back in (clean the plug first and don't over-torque it). Make sure that you're refilling with the right stuff!!!! It needs to be Type F Transmission Fluid. There's a couple of different kinds of trans fluid so make sure you get the type F stuff! Best thing I've found to fill it with are 2 bathroom size, 3 ounce Dixie cups (fill each to within a 1/4 inch of the top) and a small funnel. Shove the funnel in the fill hole and carefully pour the 2 cups of fluid in. You want it filled up to that fill hole. If a little drips out that's fine - it means it's full.
Good luck and have fun : )