You can essentially book a cheap flight around your dates of travel and then switch to a more expensive date of choice for absolutely free, no change fee or difference fee.
Dates from 6/7-8/10 works on most routes for free changes. Free changes will be allowed within 2 weeks of your eligible flight for Each change
Origin and Destination need to be the same as original
Example: Book a $106 flight and change for free onto a $426 flight
Once booked, go into details on the mobile app. Click on the red banner on top, then select the flights you want to change to