Did you do the "Easy" one-click install?
At any rate, either way, you can edit the text you're talking about by going to "Administration Control Panel". You can get to it by either going to the link that appears at the bottom of the forum pages when you're logged in as the admin user, or by going to "forum.mydomain.com/adm".
From there you should be in the "General" tab.
From there click on "Board settings" in the left-nav.
The site name and description should be editable from there. Make sure to "submit" your changes.
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