1) Sign in to Google Admin Console
2) Then click on Users Icon
3) You will see number of user in this option, click on one email ID which you want to rename.
4) Then right hand top side, click on rename user
5) A display name consisting of a first name and last name and user name that appears before the @ sign in his or her primary email address.
6) You can change either or both of these name. You can't change your own user name.
7) If your Google Apps account includes multiple domains, you can change the domain name by selecting it from the drop-down list
8) Then click on Rename User.
9) It can take some time for a new primary address to be reflected throughout the system.