At 500 gal I doubt it weighs that much. I loaded a 1000 gal Zero and it was under 1000#. However, try some channels like sapsucker78 suggested. Get some help there and a couple of 2x6's to pry with. Use come alongs from any sturdy anchor point.
I have now moved 3 tanks, a 415 Sunset, a 545 Sunset and the 1000 Zero. With each move I estimated too high and planned how to move it and each time it proved to be easier than I envisioned. Just think the move out and a few helpers will do fine.
On my last one, the 1000 zero it loaded fine because it was outdoors and the seller had a BIG payloader. On the unload end I did it with my mini excavator with no problem. The mini weighs 8000# and will lift 2500 2 feet out from the blade. I put straps around the tank and hooked them to the bucket. I then lifted the tank at about 8' out in front and held it while I pulled the trailer out from under it. There is no way it could have weighed over 1000# or the mini would have tipped that far out. Based on that I'll bet your tank weighs about 500-650#. Remove any extra weight you can first. On my sunsets I removed the agitators, lids and paddles. This was before I had the Mini.
Dave Klish, I recently ordered a 2x6 wood fired evaporator from A&A Sheet Metal which I will be converting to oil fired
Now have solar, 2x6 finish pan, 5 bank 7x7 filter press, large water jacketed bottler, and tankless water heater.
Recently bought another Gingerich RO, this one was a 125, but a second membrane was added thus is a 250, like I had.
After running a 2x3, a 2x6, 3x8 tapping from 79 taps up to 1320 all woodfired, now I'm going to a 2x6 oil fired and a 200-425 taps.