To change your seat from Main Cabin to First Class on American Airlines in 2026, you have three primary methods: Instant Upgrade with miles, In-app offers, or Systemwide Upgrades. The most common way is to open the American Airlines app or visit aa.com and look at your trip details; if seats are available, you will often see a "Load-side offer" to upgrade for a discounted cash price (e.g., $150–$300). Alternatively, you can use 15,000 miles plus a $75 co-pay (for most domestic routes) to secure an upgrade, provided the "A" or "C" inventory is available. If you hold AAdvantage status (Platinum or higher), you are eligible for complimentary "auto-request" upgrades that are cleared starting 48 to 120 hours before flight time based on availability. Note that "Basic Economy" tickets are generally ineligible for any changes or upgrades. If you have a standard Main Cabin ticket, the most reliable way to guarantee a First Class seat is to "Change Trip" and pay the fare difference between the two cabins directly.