The only way you can do this is if Expedia agrees to release your reservation back to
DCL, then you can transfer it to DU. Alternatively, if you are more than 60 days out, you can cancel your reservation thru Expedia and book thru DU. Unless you are wanting a special cabin, you might re-book before you cancel, just so you are sure of availability. This, of course, will tie up some $ on your credit card till you get the refund...issued by DCL to your card if you booked that way. Takes a few days....