That's one heavy tank. It's the 42" height. and the need for super-thick 3/4" glass panels, that makes it so heavy.
I moved a 150G Tall (48" x 24" x 30") down a set of basement steps with my son. If the 150G was a standard 72" tank length, it would have been much easier, because the glass panels are thinner (lighter). To get it down the steps, we slide it over the steps. I had the dangerous position of being in front of it. My 230 lbs of body weight was just barely able to keep the tank from crashing down on me. If I had slipped or stumbled on a step, that would have been the end of me.
In hind sight, we should have tied a rope around the tank and wrapped the end of the rope around a plank in the door way. That way, my son could have held the rope and let it move a few inches at a time.
Good luck and be careful.