Enlist two other people to help you move the heavy object.
Remove any shelves, drawers or other compartments, or loose pieces from the item; they could fall out during the move.
Place two long boards down the flight of stairs to create a ramp. Slide the heavy object down the boards slowly, with one person at either side at the front and the third person at the back. Having two people at the front is important, because gravity is forcing the object down, making the front end heavier. Alternately, place the object on a heavy, strong blanket. Ease the object down the stairs, with one person holding each end at the front of the blanket and the third person holding both ends of the back section. Pull the blanket up over the lower end of the object to keep it in place and control the speed of movement.