The steps are:
1. Chagne your DNS server settings at your registrars website to:
ns1.sophiosoft.com
ns2.sophiosoft.com
ns3.sophiosoft.com
ns4.sophiosoft.com
2. Login to your Sophio support account and find the option to 'upate store' - enter the new domain name and click update!
Here's a video you can watch that walks you through it - http://www.youtube.com/watch?v=ukXfLKxDCrY