By default, Windows 8.1 has hidden Libraries. If you want to get it back, open File Explorer and you will find the newly renamed This PC view. Here, select View, and click on Navigation pane. Lastly, enable the option to Show Libraries.
Delete Old Windows Installation Files
When you upgrade from an old version of Windows, Windows keeps a C:\Windows.old with your old files. You can delete this folder to free up some storage space. To do this, Search for Disk Cleanup, and click on Free up disk space shortcut. Next, click on Clean up system files, enable thePrevious Windows Installation(s) option, and run a disk cleanup. If this option does not appear, that means there is nothing to clean up.
Tips by Hongkiat.com