Hi
To remove one of the operating systems you need to install "EasyBCD" and use it to remove the one you don't want from the boot menu.
If you don't do this your computer won't boot and you will have big problems.
Once you make sure that the computer boots directly into the copy of Windows you want, you can just delete the other one.
Be sure that it doesn't ask with one when you boot it up, and loads directly
Mike