Manually delete the GRUB EFI boot entry and/or set the Windows bootloader to the first position before you get rid of Ubuntu. Run these from an elevated Command Prompt :- bootsect /nt60 SYS /mbr

So, what's the better way? For Legacyīoot to Windows first and use the bootsect tool to replace the GRUB boot sector with the Windows boot sector, and then delete the Ubuntu partition. Here is a similar question that can help in this case. You'll most likely end up in a GRUB command line prompt on the next boot, from where you'll have to boot to Windows and delete the GRUB EFI Firmware entry or change the order to put the Windows bootloader in the first place. If you install in UEFI mode and then delete the Ubuntu partition You'll need a bootable recovery disk (either Windows or Linux) to help you restore your Windows boot sector. You'll most likely end up in a grub rescue prompt on the next boot. If you install in Legacy mode and then delete the Ubuntu partition Note: Irrespective of which mode you install in, if you simply delete the Ubuntu partition, it won't make the Windows bootloader default automatically. There is a similar question that you can follow to check whether you are using Legacy or UEFI. (If your PC is manufactured in the last 5-6 years, and came pre-installed with an operating system, it will most likely be UEFI.)

This depends on whether your operating systems are installed in UEFI mode or Legacy mode.

Repair windows after office uninstall