A Site Collection Administrator has the greatest level of access in a SharePoint site - higher than owners with Full Control permissions. They can access everything in a site collection and do anything without being explicitly added to a site security group.
Every site collection requires at least one person to be a Site Collection Administrator. Secondary admins have the same level of access as the primary admin.
If admins need to be removed or added, there are two methods to update the role:
Follow the steps in this video.
Note: to perform the steps, you must be a Site Collection Administrator. If you aren't an admin, contact the site admin to follow the instructions. If you're unsure, e-mail EASI SharePoint Support.