How do they get the cranes down from skyscrapers?

The main crane has to haul a smaller crane-like contraption, called a derrick, up to the rooftop, where it's bolted to the building. The crane is then disassembled into chunks small enough for the derrick to painstakingly lower, piece by piece.

How are cranes taken down?

The mast itself and the base of the crane are lowered down by the same hydraulic rams that lifted them up, with each level of the mast being taken apart before the base is lowered. To remove the second crane, a third crane is often sent up, even smaller, to lower the pieces of the second crane down.