From time to time you may need to remove your radiators, be it for decorating or plastering. This is easy, but depending on size and weight you may need help with lifting. It is also a good idea to put down a dust sheet to catch any little spills.
Isolate the radiator at both radiator valves - located each end of the radiator.
Drain water from radiator. This will make it lighter to carry and decrease the chance of spilling its contents.
Once fully drained undo both tail-piece unions.
Lift off radiator (with help if necessary and following manual handling guides) and place safely out of the way while you carry out the work.
Allow the radiator to cool before you work on it by isolating it in advance.
Make sure you lift correctly, seeking out help when necessary.
Some tradesmen "thumb" the radiator, carrying it out side to drain. This is not a good idea if the radiator is hot or your thumb cannot seal the tail-piece properly.
If one of the valves are passing you can either cap it or you may have to fully drain down the central heating.