How to find this tool:
Tools > Secure Erase
When you delete a file, Microsoft Windows just removes the directory information used to find it. The actual data still remains on your hard drive, and potentially available to someone with recovery tools.
After switching on this feature, mark the radio button to indicate what level of security you want from Secure Erase.
You can then take advantage of this feature by right-clicking any file and selecting the Delete with Secure Erase option.