as thukka said, factory restore setting is the best way to go. Or just back up your all information and upgrade to whatever Windows OS you want to and your problem will be gone. Because, for your advantage, when you install window OS, window system will make sure that all other OS in that system is wiped out. Its Windows monopoly. Ubuntu will modify the grub to make the system dual boot only if you install ubuntu after window , but other way around will not work. So upgrade your window, it should wipe your existing ubuntu.