Okey, here is a short tutorial on how to do it (not the quickest way, but it's more simple that editing the registry, and also safer).
1) Download and install
CCleaner.
2) Open CCleaner, go to Tools (on the menu left on the screen), choose Uninstall (should be selected by default), find the program (Halo) in the list and click Delete Entry. The effect is the same as doing it using regedit.
3) Uninstall CCleaner (if you want, it's kinda useful).
Hopefully this helps
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