If you want to keep the existing Ubuntu system, replace the drive with a new drive and install windows to that.  Otherwise, you can re-format the existing drive and install windows.  Windows does not like to install next to Linux but it works pretty easily the other way around, windows first and then Linux, if you want both.

Thank you for responding. This is a brand new computer for me. I have no files on it. I know nothing about Ubuntu os. Removing it would be fine. I will be purchasing a Win 11 computer in October. This is to get some work accomplished with Microsoft Access until October. How do I install Win 10?

How do I reformat the existing drive? Would I be able to use internet to download Win 10?

You will need to do the following:

1.  Download the windows 10 .iso.  I downloaded mine from Microsoft a while back.
2.  Download and install a utility to create a bootable USB drive like Balenta for Linux or Rufus for windows.
3.  Run the utility to install the .iso file a USB drive and make it bootable.
4.  Go into your computer's bios menu and change the boot priority to make it try to boot from the USB drive before the hard drive.
5.  Install the USB drive and restart the computer.  If everything works correctly, it should boot from the thumb drive into a windows set up menu and walk you through the set-up.  You have the option to re-format the hard drive in the advanced windows set-up.

Personally, I would recommend watching some videos of each of these steps before trying it so you can see what to expect.  Some of these steps cannot be undone.  All of the downloads should be able to be done with the Linux system that you have running now, if you don't have another computer to work from.  Once you format the drive, the Linux system will be gone, but once you get that far, windows should be ready to load.