When you go to User CP and select "Edit Newsletter Preferences" you should see the following panel.
The Name and Email info should be filled in already. You can not change the email address AFAIK. The update button below this area is to do that. You want to scroll down and find the entry for the Montana Owners Forum. Click on it and then further down is the "Update" box you want to click.
Unfortunately, we can't see, or change, this for you. If this doesn't work, let us know and we will get the support folks involved.