You can modify existing admin group definitions and delete unnecessary admin groups on the Manage admin groups and permissions page.
To edit an existing admin group, go to Settings → Admin groups on the menu, and click Edit next to the selected group name. On the Edit admin group page, you can modify the settings the same way as when you created the admin group. For details, see Creating a New Admin Group.
To delete an existing admin group, click Delete next to the group name on the Manage admin groups and permissions page. You will be asked for confirmation. Click Yes to proceed with the deletion.