To upgrade on American Airlines, you have several options. Use AAdvantage miles to request an upgrade by logging into your account and selecting your flight. You can also bid for an upgrade through the airline's "Bid for Upgrades" program, where you offer a price for a potential upgrade. Another option is to purchase an upgrade directly, either at booking or during check-in if available. Elite members may receive complimentary upgrades based on availability, especially for domestic flights.