Yes, you can upgrade from United Economy to a higher cabin such as United Premium Plus or United Polaris business class, though the method depends on your ticket type and status. The most common way is using MileagePlus Miles or a combination of "Miles + Co-pay." If you have Premier status, you may be eligible for Complimentary Anniversary Upgrades on select domestic routes. Additionally, United often offers Cash Upgrades within the mobile app or at check-in; these are "instant" and can sometimes be significantly cheaper than booking the premium seat originally. For international travelers, PlusPoints (exclusive to Premier Platinum and 1K members) provide a flexible way to request upgrades. It is important to note that "Basic Economy" tickets are generally ineligible for any type of upgrade, even if you are willing to pay. To increase your chances, check the "Upgrade Standby List" in the United app starting 24 hours before departure, as this shows exactly how many seats are open and your current position in the queue based on your fare class and loyalty tier.