Same name but different email addresses

Same name but different email addresses

Hello, I'm having a problem with managing the names of users in my organization, one of the examples in the attached screenshot shows that when i changed an email for one of the users the old email stayed but shows the correct name on top of that it also shows the new email with the correct name! i want to know how to remove the old email address (note that i have set the new one as the primary email and set it to be the default mailbox).
cheers.