Was this your only Linux install and you are trying to change your system back to use solely Windows?
If so, I always have to use diskpart in windows to remove the Ubuntu option after Ubuntu is removed, the method I use is detailed here: linuxbsdos.com
- run powershell as administrator
- start diskpart utility with
diskpart
- list connected drives with
list disk
- select the disk that hosts your windows OS with
sel disk #
- list volumes on selected disk with
list vol
- select the volume with filesystem FAT32, there is probably only one
sel vol #
- assign a letter to the selected volume with
assign letter=D: *if D is already used, use a different letter, just remember what you used and use that letter instead of D for later steps
- exit diskpart with
exit
- now that your volume with GRUB has a drive letter, change to that directory with
cd D:
- list all entries in that drive with
ls *EFI should be listed, if it is not and you have multiple FAT32 volumes on your drive try the other volume or you are doing this in the wrong drive.
- move to EFI directory with
cd EFI then check entries with "ls"
- assuming ubuntu shows up, type
rmdir /S ubuntu and confirm with y after entering
- list entries in drive with
ls to make sure ubuntu entry is gone
- reboot system and the boot menu option for Ubuntu should be gone, as should the assigned drive letter
Update
You should be fine to remove all GRUB options however, it would be a good check to make sure that date of last write predates your current working installation date of Ubuntu. But ultimately, Windows doesn't need GRUB and if all you have on that drive is Windows, anything with GRUB in the name should be able to be removed safely. Another good check would be to make sure you can boot the external drive without your Windows drive. !remember to always back the files up before you delete them!
