Before deleting Windows.old in Windows 10
Typically, that special folder was created when you upgraded to your previous Windows. Check this BEFORE you delete it ...
Click the RIGHT button on the Windows Start menu and choose File Explorer.
In the new window, click on the left in This equipment. Then enter right on disk C :. The Windows.old folder must be inside it. Open it
Thoroughly review everything in the subfolders of that folder. Especially that of "Users" or "Users" (you do not have to check the Windows one). Copy elsewhere out of it everything you want to keep.
Steps to erase it
Click on the RIGHT button in Windows Start and choose Control Panel. Then click between its categories on the right in the System and security.
In the new window, click on the bottom right in Administrative Tools.
A list of them comes out. Double-click on Disk Cleanup (if necessary choose the C: disk in the window that sometimes appears).
On your main screen, click on the button Clean system files (choose disk C again if necessary).
The Liberator analyzes the equipment. At the end, a list of "Files that can be deleted" appears. Search in it Previous installations of Windows and click on its box to select it. Also mark Windows temporary installation files if it is listed.
Erase those files will NOT be able to return to Windows 7, 8 or 8.1 from Windows 10. Do not continue unless you are sure you want to delete them even knowing that.
Go ahead with the deletion by clicking on the OK button below. Confirm the notice that you want to do it.
Follow these steps to improve the performance of Windows 10.
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Check that your disk is fine.
Optimize your hard drive.
Why should you delete that folder?
There are two main reasons why you should get rid of Windows.old at some point:
It takes up a lot of space on your hard drive. Getting rid of it will leave you free to use it however you want.
It includes things that no longer serve you. After saving what you are interested in, it no longer has any function. Except if you want to go back to a previous Windows.
After about 28 days after installing Windows 10, the Windows.old folder is automatically deleted. From that moment you can not use it to recover your things from it or to return to the Windows you had before.
If you do not urgently need free space, it is best to keep that folder for two or three weeks. Until you make sure there's nothing in it that you need. It is usual for example to forget games of saved games that are usually in the game folder in Program Files.