As I said, you need to READ the answers, not just glance at them.
Bongoboy's link provides FREE instructions on how to format your drive, and then goes on to OFFER some software that will wipe it securely, if you happen to be selling.
Peanuts' instruction says :it will then give you the option of deleting the partition" - obviously peanuts means that you choose this option, and then create a new partition to replace it, at which point your entire existing installation will be zapped and the drive will be reformatted.