If you try to delete the Windows.old directory using File Explorer, the OS will prevent you from doing so.
If you have upgraded your PC from a previous version of Windows to Windows 10 without first of all formatting the Hard disk drive, the installation wizard will create a folder containing files of the previous version of Windows in a folder named “Windows.old“.
This windows.old folder will help you revert to the previous version of windows at any point in time but the downside about its creation is that the Windows.old folder occupies a lot of space on your Hard disk and if you are satisfied with your current Windows 10, there is no reason why you shouldn’t get rid of the Giga-bytes consuming Windows.old folder.
Windows.old directory are considered to contain system files. You could bypass the rules that prevent you from deleting after meddling with permissions settings, but there’s no need to do that. Here’s how you do it:
Removal in 5 Steps
Step 1. Go to Start and type ‘Disk Cleanup’.
Step 2. Open Disk Cleanup and select your main system drive.
The tool will scan your drive for unnecessary files and old cached data. However the Windows.old directory won’t be accounted for.
Step 3. Select the option “Clean up system files” near the bottom of the window. Select your main drive again and the scan process will be repeated.
Step 4. The result of the scan will display different types of data, from Recycle Bin files to temporary internet cache. This time around, “Temporary Windows installation files” will be there, accounting from as little as 9GB to as much as 25GB, or more.
Step 5. Select all the files you want to remove, including the Windows installation files. Click OK. Then confirm the subsequent prompts.
If you are using a modestly sized SSD, I’m sure you’ll appreciate gaining the extra space back.
Source : TechSpot