CCleaner has an option to securely erase temporary and to wipe free space on a hard drive.
Alternatively, you can use a program called Eraser to erase free space on your hard drive and to securely erase files.
You can also download Darik's Boot and Nuke (DBAN) to securely erase your entire hard drive. If you use DBAN, though, you will have to reinstall Windows or another operating system on it as this will erase everything on your hard drive.
Also, CCleaner is free to use, but you can donate. Eraser and DBAN are also free to use.