Originally Posted by
Mwenenzi
The general rule is you can only upgrade a flight operated by & with a flight number of an airline with the miles/avois/points of that airlines freq flyer program. There are exceptions such as the BA/IB/AA arrangement. So for MEL-LAX only possible to to use QF points on the QF flight number (but the chance of an upgrade is very low to nil)
Even though not relevant to OP, one can use CX miles to upgrade on AA and BA, but not vice versa.