The best way is to click the unsubscribe link in any of the newsletter issues that you have received since January 1, 2012. When unsubscribing, enter the new address and a short comment into the "I am unsubscribing because" box.
Alternatively, you can also reply to any newsletter issue received after January 1, 2012 and indicate your new email address in your email. We will then update your subscriber email address manually.
We will confirm by email in both cases.