Go to the Group's home page and click on "quit group" red circle with a white x over on the far left
Leave a group

april 2010 i accepted invite to join a group. it never got off the ground, at all .... and i now seem to be chiefadministrator of 3 members! the "quit group" option simply does not work. how can i leave this totally inactive group?

Ask the staff to delete the group via Help & Support although I'm not sure if they will if there's more than one member. As an SA I think you can expel the other members BUT if you're really cautious you can check with them first or just give 'em the boot if there's been no activity for several months or more IMHO.
How do I leave a group?