How to delete people from invitations list?

Hey, i do run a small guild and there are some people i invited, who never accepted the invitation.

Somehow these people use a member slot without even beeing in the guild. So now i need to buy new slots for new people although there are 6 open slots and Stats say, its 14 members.

Is there a way, to refuse the invitation or somehow delete it?

Thanks a million.

V