You can subscribe to the newsletter on the front page (scroll down and look on the right). To change your email address on the forum, look at the top left for "My Profile (edit)" and click edit. In the left pane you'll see "Edit Email & Password".
Matt's instructions are perfect. In case you are already subscribed to the newsletter but want to change the address at some point, at the bottom of the mailing there is a "manage subscription" link that will let you do just that.