I am planning on flying LAX>Papeete in December. I see that there is a Qantas Flight (on an Air Tahiti Nui aircraft) on that day. Can I use BA Miles to UPGRADE from economy to Business (paying for the economy ticket)? I don't know if it's possible to use miles to upgrade and I also don't know if it's possible to use them on an Air Tahiti flight (even though it is a Qantas Flight # etc.).

Thanks for the help!