Can I Upgrade to Business Class United Airlines?
Passengers can make an upgrade to the business class flights of the United Airlines. You can make Upgrades on United Airlines using the miles, place a bid, or pay in cash during check-in at the airport. After upgrading, you can get several benefits, such as priority boarding, spacious seats, or delicious meal options.
I used miles to upgrade once, but only got the upgrade right before boarding since it depends on availability. Being a higher-tier member seems to help get cleared earlier.
I once had better luck upgrading by checking availability through my United account a few days before the flight. If you're seeing high upgrade costs or waitlists, you might want to check options at https://travelbusinessclass.com — I’ve found deals there that were way better than what the airline showed me directly. Sometimes calling United after finding better rates helps too.