To comfy the customers with travel experience, United Airlines allows them to update their booking anytime before departure. But one might have to pay for United Change Flight, if they do not meet the restricted terms to change the flight. 

Here are the following terms, one should follow and prevent United Airlines Flight Change Fees.

• United Airlines does not charge a fee for changing the name, and date.
• Customers are liable to pay the difference amount while upgrading the class.
• If someone add-on the seat selection service in advance and after booking, they are liable to pay the fee for selecting the seat on United Airlines Flight.

How Much Does United Airlines Charge for the Change Flight?

United Airlines has permanently waved off the penalties of the change flight for Economy, Economy Plus and premium cabin travelers within the United States. Although, you might have to pay the difference amount during the seat upgrade or add-on service. 

Source: https://www.zupyak.com/p/3336345/t/does-united-airlines-allow-the-customers-to-change-once-reserved