You cannot change your username, but you can change your contact email.
We cannot change usernames, but you can update the contact email by following the steps below.1) Login and click the "email alerts" button from the My Portfolio page (see image below)
2) From the new popup box, click the "Email Address" dropdown (see image below)
3) Enter the email (or secondary email) you'd like to receive portfolio alerts at (see image below) and click "Update"