I used to be a tyre fitter, unless you are confident to take this on, I think would be better left to a tyre company, only you have to be sure is jacked up safely, (not always easy on a tractor) other wise assuming is a normal tyre/wheel fitting,once jacked, air let out and the beads broken , should be able to access the tube(assuming not tubeless) remove and replace the tyre if this is what you require? After you have changed the tyre, be sure the tube valve is facing the correct way, else will tear off when inflated.
vic, October 2008