I have no experience with this machine - or any commercial machines - but if the showerscreen arrangement is anything like the VBM DS my housemate has, the whole thing is held in place by the rubber gasket. Once you get that out - which can be a huge effort, especially if its old and perished - the shower screen will essentially come out too.
Youll more than likely need a new gasket because getting the old one out will damage it. the easiest way to remove it is to screw a screw into the rubber and pull on that. My housemates gasket came out in pieces, and that would only have been a year old or so.
Hope that helps.