Upgrade policies and ways to upgrade coach flights are specific to the individual airline you're flying. In your earlier thread about a similar question flying AA, you received some answers similar to the ones here. Assuming that your Dallas - London flight is on AA, and you still have unanswered questions, I'd suggest posing them in your earlier thread here:
http://www.flyertalk.com/forum/ameri...-upgrades.html


Meanwhile, I'll close this thread. If your travel is not on AA, please let me know and we'll discuss the best forum to use. Ocn Vw 1K, Co-Moderator, TravelBuzz.