An account email can be changed via the "My Account" page on each game website. Simply click the Account link on the top nav bar and then select My Account. After logging in you will see an option to change email on the left after verifying your account.
An account email can also be changed upon request by contacting support via the support website here.
Alternatively you can make the request by sending an email (using your current account email) to firstname.lastname@example.org.