I just had the wheels off of my JD 3720 last weekend. I even tried weighing them as they are filled with windshield washer fluid, my one portable shipping scale has a 400 pound capacity, and it errored out so they are more than 400lbs for certain.
The 'trick" is to never let them fall over, and have an extra set of hands if you can. Using a bottle jack, I lifted on side till most of the weight was off, the removed the lug-studs, then raised a bit more till I could 'walk' the wheel off of the center hub using a side-to-side wiggle motion. Once clear of the machine, roll them away and lean on the wall or another immobile object so it can't fall over. Finally, raise the jack more and place a jackstand under the hub to support the weight of the machine.
To reinstall them, reverse the procedure after removing the jackstand, be very carful to lowering the jack so it moves VERY slowly and controlled so you can wiggle the wheel onto the hub again.
It can be done safely, just take your time, have good equipment (jack in particular), and get help if you can.