uninstalling-ubuntu-using-windows10.md

Remove Ubuntu partition and follow the instructions below, Source: https://askubuntu.com/a/869888

This answer is for those with UEFI who have deleted the Ubuntu partitions before removing grub

You will be doing this from Windows 10. No bootable media required.

Where bootrec /fixmbr, bootsect /nt60 and the Ubuntu live with the boot-repair suggestions have failed, this has worked for me:

(This answer borrowed verbatim from here)

1. Run a cmd.exe process with administrator privileges
2. Run diskpart
3. Type: list disk then sel disk X where X is the drive your boot files reside on
4. Type list vol to see all partitions (volumes) on the disk (the EFI volume will be formatted in FAT, others will be NTFS)
5. Select the EFI volume by typing: sel vol Y where Y is the SYSTEM volume (this is almost always the EFI partition)
6. For convenience, assign a drive letter by typing: assign letter=Z: where Z is a free (unused) drive letter
7. Type exit to leave disk part
8. While still in the cmd prompt, type: Z: and hit enter, where Z was the drive letter you just created.
9. Type dir to list directories on this mounted EFI partition
10. If you are in the right place, you should see a directory called EFI
11. Type cd EFI and then dir to list the child directories inside EFI
12. Type rmdir /S ubuntu to delete the ubuntu boot directory

Assuming you only ever had two operating systems (Win 10 & Ubuntu) you should now be able to boot directly to Windows without hitting the black grub screen.