That is one of the problems with cruise line air; the flight choices are often not the most convenient. You may be able to change them, but will probably have to pay extra for what is called "air deviation," which simply means you are asking to choose a flight instead of taking what the cruise line gives you. Ask your TA what the charge is. It may be worth it, just to be more comfortable in your travels. Have a great cruise, whatever happens with your flights!