It seems that you're the only owner left so you can't leave.? You'd need to delete it at the bottom of the settings page.? Go to the Home page of the group to see if there's an Owner badge next to the Home item on the left menu.? You can always go to the Admin > Members page, then select Moderators from the Members dropdown to see the status of any remaining.? If there are no other owners and you can't delete the group, you'll need to contact Support.
Duane
--
Help:
/static/helpGMF's Wiki:
/g/GroupManagersForum/wikiSearch button at the top of Messages list
A few site FAQs:
/static/pricing#frequently-asked-questions