If you have a external drive or a spare one, hook it up. Most programs have a "backup" option for it, when it does that it compresses it (makes it smaller) and places it on the disk you choose. Most games have it as well, but that would usually just be the save file, but that is still good. I don't know if you are a gamer anyway, but if you use steam there is a backup (it does the hole game) section on that as well.
The backup is usually on the start bar, but if it's not you will just have to look around.