When you upgrade to Windows 8 the OS will back up your old system files to a folder called Windows.old. You may notice that this folder takes up a lot of disk space and can not simply be deleted using file manager. Taking control of the folder will not work either.
There is a correct way to remove this folder using Microsoft's built in Disk Cleanup tool.
To run the tool log on to your Windows 8 computer as an administrator. Move your mouse down to the bottom right hand corner and right click. Then left click on the All Apps Charm. Scroll to the right and you should be able to see Disk Cleanup under the Administrative tools menu. Click on that to start disk cleanup app. If you can not find the Disk Cleanup shortcut icon you can create one by moving your mouse down to the left corner in the Windows Menu and clicking on Desktop to go to the desktop. Right click on the desktop and choose New and then Shortcut. In the shortcut location dialog type in:
"%windir%\sytem32\cleanmgr.exe" (without the quotes)
Name the shortcut Disk Cleanup and click OK.
Now you can click on the shortcut to open the Disk Cleanup tool.
CAUTION: Before you use Disk Cleanup, make sure that all of your files and settings are in Windows 8 where you expect them to be. Deleting the Windows.old folder can not be undone!
After starting Disk Cleanup if you're prompted to choose a drive, click the drive you just installed Windows on, and then click OK.
In the Disk Cleanup dialog box, on the Disk Cleanup tab, click Clean up system files button in the bottom left of the window. As seen below.
Disk Cleanup will most likely restart and if you're again prompted to choose a drive, click the drive you just installed Windows on, and then click OK.
Now in the Files to delete section look for and Select to put a check mark in front of the "Previous Windows installation(s)" check box, and any other check boxes for the files you want to delete, and then click OK. You might want to delete the previous installation log files also.
You will now get a new message that appears, click Delete Files and disk cleanup will run and delete the Windows.Old installation for you. I suggest that you restart your computer after the Windows.Old installation is done being removed. This method also works if you upgraded your computer from Windows XP to Windows 7 and want to delete the Windows.old in your Windows 7 installation.