To upgrade to First Class on United for free, MileagePlus members with elite status—such as Premier Silver, Gold, Platinum, and 1K—are eligible for complimentary upgrades on domestic flights, space permitting. These upgrades are prioritized based on status level and fare class, with higher-status members receiving priority. You can increase your chances by booking early and choosing f... https://eexpedia-air-flights-tickets.us/how-to-upgrade-to-first-class-on-united-for-free/