Welcome to FlyerTalk, johnhuy. The classic UA fare class post is ozstamp's at
http://www.flyertalk.com/forum/showthread.php?t=113792 . Award tickets come out of their own fare buckets, not the revenue buckets, and upgradeability of a fare depends on the region (e.g. intl vs domestic), the elite status of the flyer, and the instrument (coupon, miles,etc).