The settings for this are located here:
In Outlook>Tools>Options>Mail Setup>E-mail Accounts button
Tick "View or change existing e-mail accounts" then click "Next".
Highlight the account for which you want to change the name, then click
"Change".
Change the name in the space provided in "Your Name" then click "Next".
Choose another account for the same actions. When done click "Finish".
In that case, unless someone else has a better suggestion, maybe you could
try the "Detect and Repair" feature under "Help". It worked great for me
when my Office products started acting badly. Particularly Outlook.
ZILLA