how do I remeve the cistern off my villers & Boch toilet ?

I have a Villers and Boch toilet which is leaking when i flush it. I have identifired that it is the flusher pipe as i have tiipped water from a bucket down the toilet and there is no leak. It is only when I flush it there is a leak. The toilet is a all in one set up where the cistern sits on top of the pan and no flusher pipe is visible. Im not sure of the model No as there is none on there. It is a duel flush.
I have disconnected the water and removed the plunger assembly (it only requires a quater turn). The cistern is loose but wont come off. At the bottom of the cistern inside it there is a round plastic assembly, that the the plunger attaches to, which it looks like it is somehow clipped to the plastic box designed for the half flush. From this plastic assembly the pipe that goes through the bottom of the cistern is attached. i cannot get the half flush box off or the cistern or the plastic assembly for the plunger. How do I get the cistern off????
P.S I Have pictures if you require them
Regards Shaun