To change your user name, you need to verify your email address first since any changes made on the account are needed to be confirmed via email confirmation.
Click the dropdown under your username at the top right corner of the page or click the "My account" Tab.
Click "My Account" > "Account details" and change the username.
Click "Confirm" and wait for the email confirmation to be sent to you (Check your Spam Inbox if you have not received anything).
Click the link inside the email to confirm the changes.
if you have any questions or concerns, please let us know. Thank you!