Q: I performed an upgrade from Windows 8 to Windows 8.1 and ran Disk Cleanup for system files, but I'm still missing gigabytes of space. How do I get it back?
A: Provided you have run Disk Cleanup and selected the option to clean up system files, and provided you checked the displayed item, most of the content related to an upgrade would have been deleted. However, several people have emailed me that they still were missing huge amounts of disk space.
After investigation, I found the guilty content was located in the C:\Windows\Temp folder. Deleting the content from C:\Windows\Temp reclaimed up to 70GB of space for some users--so if you're missing space, check C:\Windows\Temp and delete the content as needed.