Site collection administrators set the initial permission settings for the entire site collection. All subsites and content in a collection inherit the permission settings selected by the site collection administrator for the top-level site. If you are a site collection administrator, this means that you are responsible for setting permissions at the site collection level. Site collection administrators automatically receive full access to all functions and websites in the site collection, without having to be explicitly granted this access again. This authorization is therefore not displayed in the standard authorizations and should only be granted to a few selected users for security reasons. A new site collection administrator can only be added by an existing site collection administrator. You can add or remove site collection administrators as follows:
1.) Click on “Website actions” → “Website settings”.
2.) If necessary, switch to the top-level website settings.
3.) Click on “Website collection administrators” (under “Users and authorizations”)
4.) You will now see all the site collection administrators currently defined for your SharePoint site. You can search for additional users via the small address book and then add them; you can revoke existing administrator authorizations by deleting the corresponding user from the input field.
5.) Finally, always click on “OK”