Depending on your settings it might be that the upgrade files are kept on your system.  Disk Cleanup for the system drive (use the "Clean Up System files" will show you where the files are used, or download WinDirStat (freeware). Scrolling through there you might see "previous install of Windows", or a huge recycle bin and or Delivery Optimization Files.  Temporary files from applications that don't clean up properly or system crash log files, it all adds up.  
I was cleaning up in some files, and noticed that my system recovery files are 175 GB. After doing some research on Google, I didn't really find any clear answers on what to do to shrink the size. Any tips or tricks are much appreciated! I am on Windows Feature Experience Pack 120.2212.3920.0 [IMAGE] (system language is in Norwegian)
System recovery files are 176 GB