I do not know this as I have never checked and I am not going to check it now either, but are there anyone left not running 8.1?
If so, you are way behind... That update should have been applied 2 months after it was released at the very latest.
Then I will advice all of you to check your hardware, if it can run Windows 10. If you have Windows 8.1, the hardware compatibility is the only reason not to upgrade.
It is important to check hardware compatibility, so head over to your hardware manufacturer's website and search the support section for your PC/Laptop for information as to compatibility (Do not take this lightly).
If it is, do the update by downloading the ISO to avoid any errors in connectivity getting in way of a successful update.
After update, if you are concerned about your privacy, come back here and read about that in this thread.
Using Windows 8.1, your computer is not as stable as when running Windows 10, but read my words: CHECK HARDWARE COMPATIBILITY.