Say, I have a Club World return purchased using Avios using a 2-4-1 voucher + hefty taxes and fees.

Now, two first-class seats have opened up on the outward leg.

I do not think it possible to upgrade the leg using Avios. But, is it possible to cancel the outward leg and rebook it in First, still using the 2-4-1voucher? And retaining the secured return leg?

Thanks,