Hi Karen - first of all, I'm sorry for your loss. My condolences.
As for fare change, it depends on the type of fare that was originally purchased, and it'll most likely be the difference in fare (if any) plus change fees. You can get an estimate by looking up what the new booking will cost, subtract the existing fare already paid, and add back in the change fee. Once you have the flight information, my personal opinion is to call to do the rebooking instead of via the web.
Per their unplanned event policy, you can request a refund of the change fee with proper documentation (e.g., death certificate) after paying the change fee.