Someone has since asked me for step-by-step instructions:

Log in using your username and password and then click “Forum” (top left of the screen). Across from the literature update, you will either see a green check (subscribed) or a black minus (not subscribed).

If not subscribed, click the black minus and then select your notification preference. Then click “Add Subscription”

If subscribed, but not receiving email updates, first click the green check to unsubscribe. Then follow the instructions above to subscribe again and select your notification preference.