If you look under the step, there is a large bolt on the front and rear of the step(7/8" if I remember right). The bolt will be towards the edge closest to the step. Take the bolts out, then you'll be able to pull the step out. You may have to lift just a little to get it to start, but once it starts it slides out very easily.
If you haven't pulled the step out before, the bolts may be pretty tight, so don't be afraid to put a little arm into them.
One thing I found out putting the step back in, the battery cable may prevent it from going all the way back in easily. Just reach up and pull the cable forward a little when you go to put the step back in, it may want to tuck under the edge in the back of the shelf when you push the step in.
2006 Gulfstream Ultra 6331
33' Super C
8.1L V8 Gas