I need it to be more professional for my business.
How do I change my user name?
You cannot change your ID name or address.
You can cancel the old account and open a new one with the desired information. Or simply open a new account with a different name and password, and use both.
Or, another option is to create an alternate E-mail address that will go to the same mailbox as your main E-mail ID.
Click here:
http://edit.yahoo.com/config/list_alias