If you installed Windows 10 version 1607 "Anniversary Update" over a previous Windows version, you might have noticed that free disk space on your disk drive was considerably reduced. When you do an in-place upgrade from a previous version of Windows, Windows 10 saves a lot of files from the earlier installed OS during the upgrade and fills your hard drive with files that you might never need again if your upgrade is successful. The reason setup saves these files is so that if something goes wrong during setup, it can safely rollback to the earlier version of Windows. However, if your upgrade was successful and you've got everything working perfectly, then there's no need to keep these files. You can reclaim all the wasted disk space by following these simple instructions.