Hello,
you can join a domain on Windows 7 Home Premium x64, sp1, but the button to change domain name you can not use. How do I find where this is coming from as I don't know who my server is or how to access some user accounts in it?
You can't/don't, because that feature is only available in Professional and Ultimate versions of Windows 7. So, you can use the anytime upgrade feature to move up to Win 7 Pro or Ultimate, but as long as you're on Home Premium you're stuck.