warm it up, park on a level surface - go up and down slowly through all the gears - leave it running - get underneath and unscrew the top bolt - if it leaks out its full, if it doesnt get a pump and pump fluid into the top hole until some pours out - screw bolt back in
Two questions...
1. How would I go through all the gears while parked?
2. Can I do it without leaving it running? that feels not so safe.