Ten days after you upgrade to Windows, your previous version of Windows will be automatically deleted from your PC. However, if you need to free up drive space, and you’re confident that your files and settings are where you want them to be in Windows, you can safely delete it yourself.
Warning: If it’s been fewer than 10 days since you upgraded to Windows, your previous version of Windows will be listed as a system file you can delete. You can delete it, but keep in mind that you'll be deleting your Windows.old folder, which contains files that give you the option to go back to your previous version of Windows. If you delete your previous version of Windows, this can't be undone (you won't be able to go back to your previous version of Windows).
Press the Windows logo key on your keyboard, then select Settings > System > Storage.
Open Storage Settings
Under your hard drive information, select Temporary files.
Select the Previous version of Windows check box, and then select Remove files.