If you have admin access to a folder or an Official Group, you have the ability to revoke admin access to that folder or group from other users. Org Admins may also do this for any group in the organization.
To revoke access, go to the Official Groups tab and click on the ellipses next to a folder or group. In the window that appears, hover over the name of the admin you would like to remove and click on the grey icon to the right of their name. Confirm that you would like to revoke their admin access. You will then see the revised list of admins.
You can also revoke admin rights over a folder from a user's profile page. To do so, navigate to the user's profile and open the Groups card. Select one or more groups and then use the Remove dropdown to revoke their rights over those groups.