While most refrigerator freezers and upright freezers can self-defrost, most chest freezers don't come with this option, especially if you have an older model.
Normally, when the time comes to clear the ice from the inside of your freezer, you unplug it, wait for the ice to melt and sop up the mess with bath towels. While you're doing all of this your food is also defrosting.
There's an easier way.
Instead of unplugging, remove the food from the freezer and scrape off patches of ice with a putty knife. You can get putty knives at most home improvement stores. They are inexpensive and will scrape off ice in large chunks so that the ice can easily be removed and plopped in a bucket.
The trick is to hold the putty knife at a 45-degree angle while you scrape to avoid gouging the inside of your freezer.