Yes, absolutely correct. If they make a major change in your flight, they HAVE to give you a refund if you want. Usually they don't want to do that, so check to see what is available with other airlines and if you can get something better, cancel and get your money back. If not, you can see if there is some other routing or dates that will work for you from Delta, as they would much rather allow you to change to something YOU want, versus giving you your money back.