I used one of these to replace a Shimano MF-HG37 14-28T freewheel with an MF-HG40 14-34T freewheel.
I pulled the wheel off, pulled the quick-release skewer out, slipped this tool in, and then, using a 10" crescent wrench popped the old freewheel off instantly.
I set the wheel on the floor standing up, as if it were on a bike, with the wrench parallel to the ground. I used my weight to turn the wrench, and the tire kept the wheel from turning. No muss, no fuss.