How can I free up drive space from the Windows installer folder without killing Windows?
Source : Super User [windows-10]
I created “PatchCleaner” to clean the windows installer directory of all orphaned files in one easy click. If you don’t trust the app to do the right thing, use the move feature to put them somewhere safe in case you need them back in the future. I have run it on multiple machines and saved up to 15Gb of space 
Run PatchCleaner after windows updates to find newly orphaned files.
I recommend you use the Move action, and move the orphaned patches to external storage, just to be safe
Known Issues (full details on website)
- Adobe Reader can fail to update after running PatchCleaner.
NOTE: as @ Feb-2016 version 1.4.1.0 is out that has a fix to allow customisable filters to exclude adobe reader from being incorrectly detected.