Ow. Get a refrigerator dolly, strap it in gingerly, enough to restrain, not enough to crack glass, lay the dolly on its back on the steps, and use ropes and a stout anchor at the top to ease the dolly down step by step by the use of strong ropes well under control. Anybody in front of it, should hold position to the side of the stairs, not in front of the tank. they could be seriously injured if the thing gets out of control. Make SURE the rope and its anchoring point can take the weight, and agree in advance, no single-handed heroics if it slips control.