Originally Posted by downinit

In case there is no upgrade option on your booking screen,you can also attempt to book an upgrade via the seating chart. Sometimes you may be able to select a seat in a premium cabin and pay for it through there. I have had situations where I was able to purchase an upgrade via the seating chart on the app, even when no such option existed on the website seating chart or the booking page for the app or the website. Also be sure to check back on a regular basis, as the price and availability of upgrades tends to change by the day. The key is to be persistent and exhaust all available options.