A rain barrel looks light until you remember that a gallon of water weighs about 8.3 pounds, which means a full 55 gallon barrel tops 450 pounds. Drain it first and the rest of the move is easy.
Pro tip: Photograph the downspout diverter setup before removing it, since the angle and height it needs to sit at is easy to forget and hard to eyeball again later.
Watch out: Never attempt to lift or tip a rain barrel that still has water in it; a full 55 gallon barrel weighs more than 450 pounds and can seriously injure your back or drop and crack.