Whenever you want to uninstall a program you need to do it right. You can remove a program using the classical method (Control Panel > Uninstall a program), or using an uninstalling tool like: Revo Uninstaller. For your problem I suggest you search for files or folders on your computer that was installed along with BlueStacks and manually delete them from your system. After that try to open the setup file and start the installation process again.