There are several ways to remove it. But it depends on what type of fluid it was loaded with, AND what you plan to do AFTER it is out.
So My question to you would be, Why are you removing it?????
If you are doing it because you dont like/want/need the extra weight, I'd reconsider that.
If you are removing it because you have to change tires, do you plan on trying to save the fluid to re-use or not? There are 4 main things it could be loaded with. Calcium, antifreeze, WW fluid, or rimguard. Do you know what is in there??
If you dont plan on re-using, and it is non-toxic, and you are getting new tires, a big hole in the tire is the quickest and easiest way.
If you plan on re-using, Jack the back of the tractor up, put the valve stem at the top, and let the air out. Pull the valve ste and attach a hose. Rotate the tire to the bottom and drain. But this will only get about 1/2 of the fluid out. To get the rest, you have to take the tire off.