If you've upgraded an existing Windows installation to Windows 8, you'll probably have a very large Windows.old folder left over. This contains the old Windows data, should you need to recover an old information. Assuming you don't, it's safe to delete and recover a significant amount of storage space. It's not possible to delete this using Windows Explorer as you'll get a number of permission errors, but thankfully there's an easy method to remove it.

To begin, search for "cleanmgr" from the start page and run the application:


Then, select the drive to clean-up (it's almost always C: ) and click OK:


After a few moments, the clean-up Window will open. Now, click the "Clean up System Files" option and select the same drive letter:


Now, you'll be able to select "Previous Windows Installation(s)" from the list, which is the Windows.old folder data. Tick this and click OK, then in a few moments you'll recover the disk space to be put to better use: