If you have booked standard flight tickets, you can upgrade to a higher class on American Airlines. If you are Upgrading American Airlines Flight with miles, you need to take the following steps:
Call the American Airlines Reservations number.
State your upgrade request.
Share your booking reference & last name.
You will be informed whether the upgrade with miles option applies to your flight booking.
If applied, proceed forward to the upgrade process.
After the upgrade is complete, receive confirmation by mail.
If you need more assistance you can contact American Airlines Customer Service and you can also read the blog by Airlines Group Travel at the given link for information.