How to change the Client Acess Server (CAS) External Domain "owa.domain.com".

I have "owa.domain.com" on my both my Legacy and New Exchange 2010 for External URLs. I am going to follow the ID: 35444434 posted. I do need help now to correctly change CAS OWA External URL to "mail.domain.com". I have looked through "Outlook Web App" , "Exchange Control Panel" and "Exchange ActiveSync" for places to change the External URL. I want to make sure that I have all the correct updates In the :Exchange Management Console".

I am not clear on the process to make the changes to the virtual directories in IIS Manager to update OWA External URL to "mail.domain.com". Could you detail the steps?