First log into your organization's portal. Next, click the arrow by your name at the top right, then Settings.
You should automatically land on the Name tab. Click on Email and Password, then enter your new email address in under the Change Your Email heading:
For security reasons, your current password must be entered as well to make the change. Once both the new email and your password have been inputted, click the Change button.
NOTE: Changes to email address must be done individually by the account holder. Organization Administrators do not have access to make these changes through the Manage -> Users section of their portal, and at this time there is not a way to automatically bulk update users' email addresses.