As an admin, you can remove other admins that manage the group.

1. Navigate to the group page.  
2. On the group header, tap Members.
3. On the Admin tab, look for the person’s profile.
4. Tap the 3 dots menu for the profile, and choose Remove as admin.
5. A pop-up will appear.  Tap the OK button to confirm removing the person as admin.  This person will be removed from the Admin tab.