If you don't find a pet-cock on the lower right or left side of the radiator, remove the lower radiator hose at the radiator to drain.
As mentioned , the tractor is probably a 2 section fluid compartment:
Under the engine's oil pan will be a plug.
Somewhere under the trans/hydraulic section/differential there will be from 1 to 3 plugs....check all 3 locations because different tractors vary in quantity and location.
On 4wd tractors, the engine usually has an inverted U shaped oil pan allowing for the front axle shaft to tranverse that distance so there are 2 drain plugs, one on each side of the drive line to the front axle.
