Have a look inside the red drum to see if you can access the other end of the metal rod - there may be a nut to undo. If not then there are two options, one it may be screwed direct into the plastic moulding - if so there will be a collar on the metal pin that will accept a spanner so you can uncscrew it , or two it is simply a tight press fit into a hole in the moulding. My best guess is that it is the last option since this is the quickest and simplest assembly method, but check the others first or you could damage something!
Richard
January 2009