You should have an access hole in the top deck of the bush hog. Rotate the pto by hand until one of the two nuts line up with the hole. I use a 1" drive pull bar with extension and socket and pull on the nut with a cheater pipe. The blade bolts are fine thread and should spin fairly easily once broke loose (but can be a pain to break free). The head of the bolt goes in from the bottom so when you get the nut off the blade should drop down. You may have to tap the bolt through from the top side, but be careful not mess up the threads. Do the same for the other side, spinning the pto until it lines up with the access hole. Installation is the opposite.
Word of caution: BE SURE TO BLOCK UP THE BUSH HOG WHEN WORKING BENEATH IT. DO NOT RELY ON THE HYDRAULICS ALONE TO KEEP IT IN THE AIR. ALSO, MAKE SURE THE PTO IS NOT HOOKED TO THE TRACTOR, THE TRACTOR IS NOT RUNNING, IN GEAR WITH PARKING BRAKE SET, AND CHOCKED ON LEVEL GROUND.