To change a user's display or username:

1. Ask the the user to sign out of his or her Google for Work account. 

3. From the Home page, click Users.

4. Click in the user list for the user you want to change and choose Rename user.

             Or from the user's account page, click in the corner of the user's profile and choose Rename user.

5. Enter the new name for the user.

You can change the user's display name (First name and Last name) as well as his or her Primary email address. If your Google account includes multiple domains, select the appropriate domain name from the list.
Click Rename User

It can take up to 10 minutes for a new primary email address to be reflected throughout the system, 24 hours for domain and personal contact changes to take effect, and up to 3 days before the user can use Google Talk. See Impact of changing a username for a complete description.