It's easy to do; you can sell over the internet through a trading website such as trademe, or to secondhand dealers, on a community event stalls or to friends.
There are even professional organisations that can help you declutter your home.
But remember, don't be rash - take your time to be sure that you are ready and really want to get rid of each item you are thinking of selling. You might be more attached to some of those old, unused items than you thought.
For more information, see: B33 Decluttering and Liquidating Your Assets.