Locate the installation file you used to install Deep Freeze to this machine. By default the name of this file is called "DF5Std.exe" for versions 5.X and "DF6Std.exe" for versions 6.X.
Run the installation file (DF5Std.exe or DF6Std.exe).
Select the option to "Uninstall"
The software should uninstall and reboot the machine. When the machine reboots, Deep Freeze should be uninstalled.