First, you can backup all of your very important files in a hard drive or a USB that has a big memory. The data that should be stored inside your hard drive are not so important data. The data that you can let go of. Do not save any personal information in your hard drive. After that, you can download a software that can be used to totally wipe out data. A recommended software would be Active Killdisk. This process is called refurbishing.
