Hi rastus, welcome to Outdoorking. The page from the illustrated parts list shows each rear wheel being attached by three conventional wheel nuts. The owner manual has a more detailed illustration. After removing the wheel nuts the wheels should slide off as in a car. Then, to remove the axle you first need to remove the split collars that hold the wheel studs, by loosening the pinch bolts.
A word of caution: sometimes Greenfield makes running changes in design, so the parts list does not entirely apply to a particular mower. In the interests of safety, please let the air out of your rear tires before you unbolt them from the hubs. This should prevent any embarrassing outcomes if your mower turns out to have split rims. The parts list shows one-piece wheels, but safe practice is always a good investment.
