Boxford VM30. How do I remove the milling head?

Hi all

I have a VM30 that has been used in a school for decades. I want to remove the milling head (see photo) to attach a drill chuck, but can't see how to remove this
It has probably never been removed before, so I guess some force might be needed, but how and where??

Thanks in Advance
Adrian

Attachment 31912

I don't think you mean the milling head, that looks like some sort of chuck. There will probably be a drawbar holding it in the spindle.