Diaphram change "Jetflow Ideal Standard". ?

Have taken out flush mechanism on Jetflow Ideal Standard Unit. Diaphram is in tatters. Have got a new diaphram. Problem is. There is a black plastic rod with the diaphram frame attached to the bottom. The rod is held to the frame by a green conical plastic part. I have been unable to prise this green part off to fit the new diaphram. Does it actually come off? I do not want to force it and get myself into more problems.