Updating to Windows 10 might have disabled/removed the Samsung Settings application which enables the function keys. In your case you should try to download SW Update from Samsung's website and install Samsung Settings and any other necessary drivers from there. If you can't get this to work, I suggest you refer to the latter pages of the 2013 Series 7 chronos / Ativ Book 8 15" owner's lounge (NP770Z5E / NP780Z5E / NP870Z5E / NP880Z5E) thread on NotebookReview.