Upgrade long haul CX redemption BA metal J to F?

I read as much as I could find and do not have a definitive answer'
I have a redemption via CX Asia Miles on a LHR to LAX flight in Business.

Is there a path to upgrade this to F, with money or Avios at any point (Asia Miles, if it ever opens, unlikely)? Bidding, at online checking, at Airport? Or is there simply no path?

Thanks.