Yes, United Airlines allows passengers to upgrade their seats using miles. Moreover, the airline provides other options such as complimentary, PlusPoint, Star Alliance Upgrade Award, and Instant Upgrades for upgrades. Moreover, travelers can request a United Airlines Seat Upgrade either by visiting the official website of United, by speaking to the customer service of the airline, or by asking for the same at the airport. For further insights related to the upgrade, visit the official website of United Airlines or read the blog at the above link.