Think the OP is asking about a paid upgrade offered at the kiosk. It's exceedingly rare - it would mean that even with every single NW/Delta elite on the plane being upgraded, there were still seats open. You can always ask if it's available, but generally first class goes out full of elites. My guess is they'd charge you something like $150-$200, which really isn't worth it. I know it's a bit of a thrill to sit up front, but snag an exit row or bulkhead and you're 90% of the way there. My vote, even if you're offered the paid upgrade, is to spend that money on something more interesting in DC.