Upgrades can be purchased through United Airlines or compiled through the Mileage Plus frequent flyer program. Upgrade certificates through United include 500-mile upgrades, which can be used on flights within North America to move up to the next class of service. If you are travelling more than 500 miles, multiple certificates must be used. Not all flights are eligible for an upgrade. For those that are, space and availability is limited, according to United.
Use United Airline's "advanced shop for flights page" if you wish to book your flight and upgrade online. Alternatively, you can call United Airlines at the number on the back of you Mileage Plus card to request an upgrade over the phone.
Shop for your flight and select the type of upgrade you wish to use. You can use a 500-mile upgrade certificate, certificates good for travel in multiple United regions or miles to pay for an upgrade. You will book your flight and select seats in the cabin (economy or business class) that you wish to upgrade from.
Check your Mileage Plus status. United bases when they grant upgrades on your level in the program. For instance, 500-mile upgrades are granted, if seats are available, 100 hours before your flight's departure time for "1K" level Mileage Plus travellers. Other Mileage Plus designations include Premier Executive (72 hours), Premier (48 hours) and Premier Associate (36 hours). All other Mileage Plus members will not receive word on their upgrade until 24 hours before departure.
