You need to provide info like flight number, date and city pairs. And tell us the exact flight number you booked it as. This is important because if you're on a codeshare (DL-coded, NW-operated or vice versa) you are basically SOL when it comes to upgrades.

NW phone agents cannot do anything about domestic upgrades, technically. There are a few who can get around this but, generally speaking, the phone agents cannot manually process upgrades. They must be done automatically.

-RM