Follow the below steps properly:

STEP - I: Deleting Ubuntu Partitions

• Boot into Windows OS




• Press Windows + r keys together and type diskmgmt.msc to enter into your disk management utility




• You can easily recognize the Ubuntu partition by their size. Another hint to recognize the partitions is to look at the partitions which don’t have a file system and drive number. Windows partition is labeled with a drive number such as C, D, E etc and are usually in NTFS or FAT file system




• Manually select all your Ubuntu partitions one by one and right click on each and select the option - Delete Volume




• All the deleted space will show as Unallocated on your Windows partition table. Now, either extend any of your existing partitions or simply create a new partition (using the entire Unallocated space you got)

STEP II: Fixing the Boot loader

• Use your Windows OS disk and restart your computer. Press F10 or F12 at the boot time to go into BIOS/UEFI and choose to boot from removable disk




• Select 'Repair your computer' option




• Go for the 'Troubleshoot' option here and then select 'Advanced options'




• Look for the 'command prompt' option and select it




• Once you enter into the command-line interface, type the following command:
  bootrec.exe /fixmbr




• Once it’s done, restart your computer and this time boot normally from the hard disk. You should be able to boot into Windows.

In case you encounter Grub rescue error, try the steps below:

• If the command bootrec.exe /fixmbr did not work, try the 'Automatic Repair' option in advanced troubleshoot option




• It will find the issue and take some time to repair it

Once done, reboot your system and you should be able to boot into Windows OS directly (with no GRUB options).