Can't change email address on My Account Details page

The email address field displays on the My Account Details however you cannot edit it. The Username field required to login is separate from the email address field so I don’t understand what you’d display the Email field but not allow people to change it. Surely you intended to display the Username field but not allow editing, and display the email address and allow people to change it.

Where is the option to enable people to change their email address?