After Booting with this Live CD, just click on the CDROM icon on the Desktop, to open its folder contents, then Right Click the zerofree.sh file and Choose the "Run in Terminal" option and then follow the instructions shown on the terminal.
As you may be aware, Booting with a Live CD, requires that you need to change the Boot Order on your System / Guest BIOS, quickly on startup, by pressing either F2 OR F12 OR F10 OR an equivalent key and then change the Boot Order to boot from the CDROM...