How do I remove a user from the Admin group?

Firstly, enter the group management page and click into the admin group:

Here you can see a breakdown of all of the users within your platform, and whether they are / aren't assigned to the admin group:

To remove them from the admin group, you need to select to remove +/or demote them from any roles allocated within the admin group - in the example above the users would need to be demoted as a supervisor and removed as a member.