We typically use the Central Administration Web site to create a site collection in a stand-alone deployment, while creating a new site collection it asks for only two Site collection Administrators (Primary and Secondary)

1. Primary Site Collection Administrator to add the user name (in the form DOMAIN\username) for the user who will be the site collection administrator.
2. Secondary Site Collection Administrator to add the user name for the secondary administrator of the site collection.

Anyhow, if we want to add (or remove) more than two users as Site Collection Administrators in Sharepoint 2010, following simple steps can be followed:

1. On the Home page of the site collection, click Site Actions in the upper-right corner of the page, and then click Site Settings.
2. In the Users and Permissions group/section, click the link Site collection administrators.
3. In the Site Collection Administrators box, type the name of the user you want to add.

   If you are adding more than one user, separate the names or addresses with a semicolon.

4. Click the Check Names icon to verify that you have entered the correct account name.

Thanks,
Nabeel Shahid.