How do you stop a facebook group being within a university?

[Alice]

I created a human rights society at my university (The University of Nottingham). Part of this involved setting up a facebook group. When I created the group it gave me the option of with creating it "within the University of Nottingham" (only members of the uni can join) or "outside the University of Nottingham". I foolishly picked the first one.

Now I have the group and several members - but I'd really like to change it to outside the University of Nottingham so more people can join. Does anyone know how to do this?

(Deleting and starting again is not an option)
NOTE: no you cannot just change it to open - it is still in Uni of Nottingham.