To start downsizing take a room at a time. Determine what is needed in your next move, what should go to charity or to a family member, and what has sentimental value. It is hard to let go but is a great feeling to purge. Once one room is completed start the next. Remember your did not acquire all those items overnight and you cannot get through the entire house in the same amount of time.
Consider this: if you haven’t used it in over a year you probably don’t need it.