As usual after upgrading Windows 10 Fall Creators, the old Windows 10 version will be saved as Windows.old in the C: drive, we will need to clean up to free up space for the hard drive. The way to clean up is the same is to Disk Cleanup but before you clean you need to note something:
What is Windows.old?
Windows.old is the directory that contains the entire old OS, and Microsoft retains it on the C: drive. There is a reason this folder will help us to restore the old version of Windows. This folder will be automatically deleted after 1 month from the date you updated to the new version. So if Windows 10 Fall Creators on your computer run unstable or you can not fix the problem, then you can use the “Go back to previous version of Windows 10” feature in Settings> Update & Security> Recovery to Back to Creators.
In addition, Windows.old also contains all of the personal data you store when using the older version. If we lack something, we can go back to the Windows.old> Users folder and find it easy.
If you want to go back to the old version and do not want to install Windows, you can back up this folder to another drive or USB drive or external hard drive. Windows.old does not allow us to move to another drive or external drive with File Explorer with normal admin rights so we can use specialized backup software like EaseUS Todo Backup. I used to use this software to backup Windows.old to the external drive.
Just download the free version, open the File Backup option, select the Windows.old folder on the C: drive and select another drive to save the backup file then click Proceed. When you need to put the Windows.old folder back to the C: drive, just select the Recovery feature in Todo Backup.
Now the entire Windows.old folder has been copied somewhere else, like the Windows.old folder on my machine has a capacity of about 20 GB, which occupies quite a lot of storage space on the SSD. Now we can safely delete this folder to free up disk space for the OS.
Hit Windows + S and look for the Disk Cleanup tool> click the Cleanup system files button.
Find the Previous Windows installation (s) and tick, but you can choose other things to delete such as Recycle Bin in Recycle Bin, temporary files, Device driver packages, Windows upgrade log files … which occupy more space> click OK> select Delete files in the confirmation dialog.