You're welcome although to clarify I didn't mean you had to actually purchase another ticket. If you do a flight search, just on that first screen that lists all the flight options, on each itinerary row should be a link that you can click on to see the upgrade eligibility/availability (barring the occasional known bug where a domestic segment is coded as business because it shares a flight number with an international flight and the system therefore incorrectly reports it as not eligible for upgrades)