Which instant upgrades are available on American Airlines flights depends on what type of classes are offered. If it is a two-class flight, you can upgrade from Economy to First Class. If it is a three-class flight, you have the option of upgrading to Business as well.
For travel in the United States and Canada, American Airlines offers a "Y-Up" fare that will upgrade you automatically. When purchasing a "Y-Up" ticket, you pay the full-fare economy fare -- known as a Y fare -- and, on eligible flights, you will be instantly upgraded to the next class of service. Y fares are fully refundable, cost less than full Business or First Class fares, and have fewer restrictions than discounted business and first class fares.
American Airlines generally doesn't advertise Y-Up tickets, and ticketing agents are not trained to offer them. You can call the airline directly and ask for the discount by name, or you can find Y-Up fares on the airline's website, aa.com.
