To the OP, welcome to the forum. Some of the responses above are a bit head scratching. Here's the reality for CX upgrades, and it's not the news you want to hear:

1) You can only upgrade one class of service on CX. BOS is a 4-class plane ("77H" in CX lingo) with Y, PEY, J and F. That means Y can only go to PEY, PEY to J, J to F.
2) You cannot use any points currency except CX Asia Miles to upgrade your ticket to PEY. Aka, you cannot use AA miles to upgrade a CX ticket.
3) You can only upgrade certain sub-fare classes, to top off the restrictions. Only economy sub fare classes Y, B, H, K, and M are upgradeable to PEY. All of the other (aka cheaper) sub fare classes are excluded. You'll need to check your ticket to see which sub fare class you bought.
4) Cash, part 1: there is presently no "let's make a deal" like US airlines. If you want to fly F, whose cost might be 10k USD full fare for the one way, and you bought an economy ticket whose value for the one way is $500 USD, you will pay $9,500 USD for the F upgrade. Aka, you pay the fare difference. You can also do this for PEY and J, where the fare difference obviously will be lower. To J, my guess is your fare difference will be in the $3-4k USD range. To PEY, perhaps under $1k.
5) Cash, part 2: sometimes CX won't give you credit for your underlying ticket. Maybe it has restrictions like nonrefundable or something. In this case, you must eat the original ticket and just buy the proper class you want at whatever rate it's going for.
6) Cash part 3: CX will be rolling out a cash bidding system for space-available upgrades, but it's not in place yet. When this goes into effect, however you can only go up one class. And F isn't included. So only Y-PEY or PEY-J.
7) Amex points: Amex points do transfer to CX Asia Miles. So, if you want to upgrade Y to PEY and you're in an eligible Y sub fare class (Y, B, H, K, M), then perhaps you do it. Read around here to see how the wait list process works.