It is not customary or necessary to remove one operating sytem in order to make space for another. If you want to get rid of Ubuntu, you can just leave it on the disk and remove or overwrite the partion from the Windows installation medium. The Windows installer will offer to overwrite anything, that it cannot handle more gracefully.
The same works vice versa, with the addition that Ubuntu also offers a nondestructive installation inside a Windows partition. Microsofts operating system is not that advanced, although the company would be free to make use of the necessary file system code from Linux.