How do I delete old email addresses that pop up in the log? A few have childhood nicknames that appear on the To line of an email. I need to change them to grownup names. How do I edit that log?

How do I delete (or edit) the email addresses that show up on the log of prior sent items? Several of the names are for childhood nicknames, and I need to have them updated to show adults--e.g., no more "Susie," but now should be "Susan." How do I edit (or delete and start over) with this log of outgoing addressees?