loosen the nuts on the wheel but leave them on
then take a large sledge hammer and wack the edge of the wheel if the wheel is hard to get off.
as for the axle leave the bolts on and do the same thing, loosen them but dont remove them, then take a hammer and smak the axle plate and it should pop loose.
Don't hit it extremely hard but give it a good bump a couple times
it will pop loose.
You might want to deadjust the shoes first too before attempting to remove the drum, if they are adjusted out it will be alot harder to pull off.
And being a large truck those drums are heavy so BE CAREFUL, get some help :o)