It would probably be best for you to call and find out.
Some flights are cheaper if they are on a "no-cancellation" policy - but I don't know if Disney, in getting blocks of seats for themselves to offer in their packages, applies that policy.
The only other possibility I can suggest, providing that you aren't worried about availability or losing a discount that you can no longer apply and you are more than 45 days in advance of your trip - cancel the whole thing and re-book from scratch without the airfare. You'll have to wait a while for the refund though.
If I'm way off base, I hope someone else can correct me, but I think this is accurate.