how to change Gmail account User Name
You can change the name that's linked to your email address, but not the email address itself.
- Open Gmail on a computer.
- At the top right, click the gear .
- Select Settings.
- Click the Accounts tab.
- In the “Send mail as:” section, locate the email address you'd like to edit.
- Click edit info next to the address.
- In the “Name:” section, specify what you’d like your name to be and click Save changes.
for more Information please visit this link.. https://support.google.com/mail/answer/8158?hl=en&ref_topic=3394465