When I encounter changes, my first step is to see what other flights are out there, and how I can improve my position. For example, if they cancelled your flight and now you have a four hour layover, find a different routing that works better for you, even if award space isn't available. Call and ask them, politely, to open up award space since they were unable to keep the original itinerary they sold you. If the agent declines, ask to speak to a supervisor to see if he/she will open up space. Plan on a real long call.
In my experience, the major airlines know if they have made a mess of your itinerary, they know they should make things right, and for me, they usually do. I act polite, ask for (not demanding) help, but being firm if they resist.