I recommend to try to do a one-way dummy booking on the qr website and pretend to buy the ticket with QMiles. If you see QMiles availability for buying a ticket, there is also upgrade availability. Sometimes the website is not showing you availability if you're entering your booking code and try to upgrade online even if there actually is some availability for your flight. In that case, explain the situation and write it to the QR Contact center, they should be able to do the upgrade if the ticket was booked in an upgradeable booking class.
Happened to me before...