Fiji Airways business class
If you're curious, Can I book a business class upgrade on a Fiji Airways flight? Yes, you might be able to do so before the flight takes off online. Therefore, it is not obvious if this alternative also entails a return for the price difference between what was actually paid and what was actually due.
A corporation called Fiji Airways provides travel options all over the world. They provide a wide range of destinations, and tickets are frequently quite inexpensive. You can view the alternatives available on Fiji Airways' website if you want to upgrade your seat.