Log in to your account with your username or old email address.  Click on Account details.
Replace your old email address with your new one.
This is also where you could change your password if you wanted to.
*** Scroll down and click on SAVE CHANGES ***

Note: Your username has not changed and as the key to your account, never can be.
Only your communications email address on the website will change.

Check that the change has been successful by logging out and logging back in with your new email address.
Take time to enter your email address and password carefully.
If you make 10 unsuccessful attempts at logging in, you will be locked out of the website for over an hour.