If not removed every few years and greases the wheels rust on.
Jack it up, make sure it is well supported then get behind and apply your biggest hammer liberally.
For you peace of mind, go to the toro web site plug in your model numbers and download the parts manual which has a nice exploded view of the rear axel.
From memory it comes off after removing the 4 small nuts, the single large one holds the drum onto the axel, rather like a trailer wheel.