Can I upgrade Amtrak tickets after purchase?
Yes, Amtrak.com gives you the freedom to make quick and easy Upgrades to existing reservations that were made online, through the Amtrak App, subject to availability. Passengers can upgrade to a higher class of service, such as coach to business or first class, by paying the fare difference. For more information, you can read the blog by AirFlyReservations at the mentioned link.
Read more:- https://www.airflyreservations.com/blog/how-to-get-upgrade-on-amtrak-train