Instructors can change their Canvas username and email address by updating their account in Instructorlink:
Login to https://instructorlink.ucsd.edu/ (this is the site you go to enter final grades)
On the left menu click on My Account
Update your email address and click Save
Note: Your email will be updated in Canvas during the next Canvas refresh (occurs 7:30am, 8:30am, 9:30am, 12:30pm, 3:30pm, 4:30pm and 6:30pm).