Hi Adrian. I'm Greg, an installation specialist and 9 year Windows MVP, here to help you.
What I'd do at this point is install Media Creation Tool from this link, choosing the button to Install Tool Now and then open the installed app and choose Upgrade This PC Now: http://windows.microsoft.com/en-us/windows-10/m...
This is the most stable way to change to the latest version (which you need anyway) and because it reinstalls WIndows while keeping your files and programs in place, fixes most problems. It also brings all Windows Updates to date.
If necessary you can use another PC to create the bootable media or download the ISO to transfer back to the problem PC and open the media or click to mount the iSO file, right click Setup to Run as Administrator.
If further problems then follow these steps can overcome them: http://answers.microsoft.com/en-us/windows/wiki...
These special steps lead up to if necessary choosing to save nothing when running the media which almost always works, and is close but not as good as a Clean Install which is also offered as an option. Your files should always be backed up if you value them at all.
If these do not help then report back any verbatim error message or behavior.
If you want to temporarily block the update then immediately after it fails try running the Hide Updates tool downloaded and installed from here: http://download.microsoft.com/download/f/2/2/f2...
If it won't find and hide the Update then you can set a Metered Connection to turn off Windows Updates for awhile until the version matures and you can try again using the method I suggest which always works best: https://www.howtogeek.com/224471/how-to-prevent...
Almost everyone with major version upgrade problems who Clean Installs the same version does not have those problems. This Clean Install should get you past all difficulties as it has hundreds of thousands of others who have followed the steps in this link and never come back to report another problem: http://answers.microsoft.com/en-us/windows/wiki...
I hope this helps. Feel free to ask back any questions and let us know how it goes. I will keep working with you until it's resolved.
________________________________________________________
Standard Disclaimer: There are links to non-Microsoft websites. The pages appear to be providing accurate, safe information. Watch out for ads on the sites that may advertise products frequently classified as a PUP (Potentially Unwanted Products). Thoroughly research any product advertised on the sites before you decide to download and install it.