I just simply search 'at&t internet settings' in google: 'http://www.google.co.uk/search?client=firefox-a&rls=org.mozilla%3Aen-US%3Aofficial&channel=s&hl=en&q=at%26t+internet+se ttings&meta=&btnG=Google+Search
Quite a lot of results I think the first one will work.