You probably can't switch at this point but its generally felt to me like there are a lot more spare biz seats on the a380 flight than the 777 flight - which I would guess increases your chance of finding an avios upgrade. If you could switch for a de minimis fee and flightstats suggested it wasn't stupid I might be tempted to do this. But as I said no idea what fare rules you're subject to....

I'm actually bringing my o/h out to hkg with me this week but she's flying back in F while I fly back in J which makes me sound very virtuous until I explain that I snagged the tix in the recent sale...