If it's the same design as the IS version (and the 400/5.6) then it's quite a simple task to remove it.
You need to remove the protective rubber from the front end of the hood. Just inside the front end there's a thin ring with several small slots (look very closely).....using a suitable tool, unscrew this ring (it looks similar to a filter thread). Once removed, you slide the remaining part of the hood backwards off the lens (having first removed the tripod ring).
HTH
Bob
Ok, got it, bloody tight is the answer!