Originally Posted by
Kiwi Flyer
A YRWSTARx fare cannot be upgraded to a higher booking class for just one flight.
Not
entirely true in the case of NZ:
NZ PACIFIC PREMIUM ECONOMY CLASS UPGRADE SURCHARGE ON- AKL - LON/LAX/SFO/YVR V.V. AKL/CHC - NRT V.V. AKL - HKG V.V. AKL/CHC - KIX V.V. LAX/HKG - LON V.V. AKL - SHA AKL - SYD/MEL/BNE NZ PACIFIC PREMIUM ECONOMY IS AVAILABLE FOR PASSENGERS PAYING ECONOMY CLASS RTW FARES THE FOLLOWING SURCHARGES USD 125 FOR AKL-SYD/MEL/BNE AND USD 350 FOR ALL OTHER SECTORS BOOKED IN E CLASS USD 170 FOR AKL- SYD/MEL/BNE AND USD 500 FOR ALL OTHER SECTORS BOOKED IN U CLASS.
So you should be able to pay to upgrade your RTW sector to premium economy, then use your M&M Star Alliance upgrade from there.