Setup Site Collection Admins
Site Collection Admins have full control over every site in the Site Collection. If a user is added to the Site Collection Admins group, these permissions will override any site level permissions. The Site Collection Admins basically run the entire Site Collection. You can create multiple Site Collections, and also have different Site Collection Admins for each of the Site Collections. Below will show you how to add a user to the Site Collection Admins group.