Method 1 (Simple): Start typing the email address, Outlook start showing the available email addresses, select it and delete. Now start using the new email address. It will be saved once you successfully send it.
Method 2:(bit more complex): The stored email addresses are in a file called “Outlook.NK2″. Use one of the following NK2 manager programs. 1)Ingressor:http://www.ingressor.com/2) NK2-to CSV http://www.epute.com/nk2csv/