Changing to another cpanel server

I want to change service providers. They currently use cpanel and whm. How do I move to the other service provider without having to redo everyones accounts manually? Do I need to be the root? I have tried this with doing a full backup and then restoring on the new server but I get the unzipped .tar file. I need to know if there is a way to put everything in place. That would include emails and databases.

Thanks!

Chris