United Flight Change Policy: United Airlines will allow you to change certain eligible flights but if your fare is not unrestricted you will be forced to pay a fee that will depend on your route. If you decide to change your flight on your own, you can do this in two ways:

Go to the United Airlines official website and click on “My Trips” to find the flight you wish to change.
Click on “Change flight.” When you decide on what you want to change about your reservation, you can search for new flights.
Here, you’ll find information on the differences in fare and if you’ll have to pay a change fee.
You can also do this via United’s mobile app. When you find your flight, tap on “Change flight.”
If your ticket might not be eligible to be changed, and if you try to change it, you’ll receive a message telling you that you can’t do this. The tickets that can’t be changed after you book them are the Basic Economy ones. These are the cheapest tickets available. You can only cancel them in accordance with the 24-hour policy.

For domestic flights, you will likely be paying about $200 for the United Airlines flight change, and for some United international flights change you could be paying up to $400.