Disinstallare Ubuntu con il dual-boot su GRUB

Per togliere ubuntu da un PC con Windows 8.x (ma penso sia applicabile a qualunque Windows):

1. Put the DVD in your optical drive and boot from it.
   
2. Press a key when it displays Press any key to start from CD or DVD.
   
3. Select your language etc. and click Next.
   
4. Click Repair your computer.
   
5. Click Troubleshoot.
   
6. Click Advanced Options.
   
7. Click Command Prompt.
   
8. In the command prompt window, type bootrec /fixmbr
   
9. Click the red X to close the command prompt.
   
10. Click Turn off your PC.
    
11. Turn the PC back on and it should boot directly into Windows.
    
12. This leaves the Ubuntu partition on your hard drive or SSD. To remove it:
    
13. Hit Windows+X and select Disk Management.
    
14. Find the Ubuntu partition. It will probably be a large partition without a drive letter.
    
15. Be sure you have the correct partition!
    
16. Right-click the partition and delete or reformat it with a Windows filesystem.
    

Fonte: https://askubuntu.com/questions/429610/uninstall-grub-and-use-windows-bootloader