Click on Participants in the left sidebar and open the Administrators tab. Then select the admin you want to delete, by ticking the box left of the admin's email address. You can now click on Delete to delete the admin.
Updated over a week ago
Click on Participants in the left sidebar and open the Administrators tab. Then select the admin you want to delete, by ticking the box left of the admin's email address. You can now click on Delete to delete the admin.