How to remove the Windows.old folder
If you upgraded to Windows 8 from Windows Developer Preview or Windows 8 Consumer Preview, and you didn't format the partition during the installation process, files that were used in your previous version of Windows are stored in the Windows.old folder. The type of files in this folder depends on your computer.
After you’ve used Windows 8 for a while—for example, one or two weeks—and you’re confident that your files and settings are back to where you want them to be, you might want to reclaim disk space by using Disk Cleanup to delete the Windows.old folder.
Open Disk Cleanup by swiping in from the right edge of the screen, tapping Search (or if you're using a mouse, pointing to the upper-right corner of the screen, moving the mouse pointer down, and then clicking Search), entering Disk Cleanup in the search box, tapping or clicking Settings, and then tapping or clicking Free up disk space by deleting unnecessary files.
If you're prompted to choose a drive, select the drive that 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.
If you're again prompted to choose a drive, select the drive you just installed Windows on, and then click OK.
Select the Previous Windows installation(s) check box, and any other check boxes for the files you want to delete, and then click OK.
In the message that appears, click Delete files.