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.