According to the United Change Flight, all the premium plus, business, first, economy plus, and economy flight passengers within the U.S. need not pay any flight change fee. This rule also applies to flights traveling within the U.S. Virgin Islands and  Puerto Rico. Moreover, this is also applicable for the flights departing from the U.S. and flying to either Mexico or to the Caribbean. Moreover, You can also connect to the United Airlines Customer Service for any queries.