This seems to have worked for me. This is a simplified set of instructions from http://www.kavoir.com/2012/07/how-to-free-up-c-drive-disk-space-in-windows-7-easy.html
- Make sure no installations are running on your machine (there's probably a formal way to do this, but I'm not sure how).
- Copy using Windows explorer C:\Windows\Installer to another disk, e.g., D:\C_DRIVE\Windows\Installer -- note: Windows\Installer is a system folder and thus invisible in Windows 8.1. You have to tweak your account to make it visible to use Explorer to make the copy. Google will help you find out how to do that.
- Make a backup copy of C:\Windows\Installer
- Type the following commands in a cmd.exe window running as Administrator:
rmdir /s /q C:\Windows\Installer mklink /D C:\Windows\Installer D:\C_DRIVE\Windows\Installer
