Upgrading from United Economy to Business Class (United Polaris on long-haul routes) can be done through several methods depending on your fare class and status. The most direct way is via MileagePlus Upgrade Awards, which use a combination of miles and a cash co-pay (often $0–$600). You can check for availability by searching for "Upgrade Awards" on the United website or app under "Manage Trips." If you have PlusPoints (earned by Premier Platinum or 1K members), you can apply those for a bump in cabin. Additionally, United often offers cash buy-up offers during check-in or within the app, which can range from a few hundred to over a thousand dollars. If you are a high-tier elite member, you may also be eligible for Complimentary Premier Upgrades (CPUs) on domestic routes, though these are rarely available for the lie-flat international business class seats.