How to remove the Windows.old folder in Windows 10

If you upgraded to Windows 10 from Windows 8.1 or from Windows 7, some files used by your previous version of Windows will be left in the Windows.old folder. Windows.old folder can take up quite a bit of disk space.

Windows.old could consume your disk space 20 GB or more depends on your previous Windows installation and how large it was. These files will be automatically removed within 28 days of upgrading, or you can use Disk Cleanup to remove them yourself.

Here's how to delete the Windows.old folder and save a lot of space.

Warning:
Before you use Disk Cleanup, make sure that all of your files and settings are where you expect them to be. Deleting the Windows.old folder can’t be undone.

1. Type "disk cleanup" into "Search the web and Windows" box and then click "Disk Cleanup".

2. Select the drive that you just installed Windows on if it is not already selected, and then click OK.

3. In the Disk Cleanup dialog, click "Clean up system files". If you're prompted to choose a drive, select the drive that you just installed Windows on, and then click OK.

4. Select the Previous Windows installation(s) check box, and any other check boxes for the files you want to delete, and then click OK.

5. In the message that appears, click "Delete files".

6. If you're prompted to confirm your decision, click "Yes".

Source
How to remove the Windows.old folder