I'm sure i'm just being dense, but I cannot see anywhere how to administrate a field group.
When editing a group (for instance : Common), I can see 'Key', 'Name', 'Expansion' and 'Status', but nowhere which fields that particular group is using.

The buttons above this area simply say 'Add a group' or 'Groups List'.

Where do I need to go to modify what fields are being used inside a group?

Thanks in advance.
Sam.