Last summer, I was stuck in a middle seat for a flight to Tokyo until I decided to try a Systemwide Upgrade (SWU). Since I’d hit the Loyalty Point milestone, I had two SWUs to burn. I called the AAdvantage desk, and since there was "C" inventory available, they moved me to Business immediately. If you don't have SWUs, the best way to modify your cabin is checking for those mileage offers in the app. Just don't wait until the gate; Business fills up fast these days!