Yes, you can upgrade from Economy on United Airlines through several methods, though the ease of doing so depends on your MileagePlus status and the "fare class" of your original ticket. The most common way is using Mileage Upgrade Awards, which involve a combination of miles and a cash co-pay (unless you booked a high-tier Y or B fare). If you have Premier status, you may be eligible for Complimentary Premier Upgrades on select domestic and regional flights, which are cleared automatically starting 96 to 24 hours before departure. Additionally, United offers PlusPoints to its Platinum and 1K members, which can be used to skip the line for upgrades on both domestic and long-haul international routes. For those without status, United frequently offers "Day-of-Departure" paid upgrades during the check-in process on their mobile app, often at a significant discount compared to the original price difference. It is important to note that "Basic Economy" tickets are generally ineligible for any form of upgrade, so always check your ticket's fine print before trying to move to United First or United Polaris.