Try using the Revo Uninstaller. It's freeware and i've been using it frequently to do clean deinstalls of registery/files for anything i don't use anymore. i've also had to use it for PSO2 to uninstall it after a failed patch/launcher denying to lauch and get it to work after a clean deinstall.

i'm not going to make promises to you here, but atleast i can tell you that it will properly delete your game files.