Assuming that this is a Chevy Express/GMC Savanna van (not the later/current Lexor on the Promaster chassis), you'll need 10, 13, and 18mm wrenches to get it out, according to some notes I have. YMMV if you don't have the rotator bases, but definitely 18mm for the bottom four nuts. I would suggest that you take out the seat only first, as I found it to be both quite heavy and a handful. Hopefully, Walter is strong and talented.
When you're done, you will be left with four studs sticking up from the floor, and they are welded in. I would not suggest cutting them off as you'll be left with no (easy and safe) way to put the seat back in, should you or a subsequent owner wish to. You could make a thick board(s) with four holes in the appropriate places, or have someone make something for you.