Your username, email and password are all managed from within the Account & password section of Settings. To update any of these, click your name on the top right and then select Account & password.
Updating your username
Click Change username. Enter your new username, then click Save changes.
Updating your email address
Click Change email. Enter your new email address, then click Save changes.
Updating your password
Click Change password. Enter your new password, then click Save changes.
Note: When changing your password, you cannot use any of your last 5 passwords.