Be careful about the "travel insurance" they offer to tack on to a ticket mentioned by TBAN--in my opinion, looking at the fine print, the rules on such insurance are so restrictive that they are not worth it. Basically you can only change for dire reasons such as death and illness (and I'm not sure but it may be only the illness of the traveler him/herself, not family members, but that may vary), it does not give you carte blanche to make a change for any reason.
Not to derail, but if you get travel insurance and have to file a claim, don't give up if your claim is denied. File an appeal, and keep at it. I had to change a flight that I had bought insurance for. To make the initial claim, I had to send supporting documents, including a death certificate stating cause of death for a relative that died, necessitating the change of flight. The insurance company denied the claim, saying that the fees incurred for the change were not change fees but a rate increase. The appeal dragged on for a month or more as I gathered supporting statements from Travelocity. I was finally successful in getting the refund, but it was a tough fight. Moral of the story: If you buy travel insurance and have to file a claim, don't give up.
Note: In my case, I had booked the flight to see a relative who was seriously ill. When he died earlier than expected, I had to change the flight. Neither Travelocity nor the insurance company questioned that the death was a qualifying event, but the insurance company, for some bizarre reason, argued that I was trying to get reimbursed for a rate increase.