While you can, download the Windows 10 ISO and put it on a USB key. USB Flash Drive - Create to Install Windows 10 - Windows 10 Forums
If you don't have a spare USB key go and buy one. 4GB is sufficient and you can get a 8GB one from ASDA or some other supermarket for less than £5 (as far as I remember around Christmas 2014). They are not expensive anyway.
The problem is 8.1 recovery partition doesn't work after upgrade to 10 so if you have Windows 10 on USB you can use that instead - either to do a repair install or (worst case) clean install.
I would also suggest (as you have an admin command prompt) making a new local administrator account right now.
From your admin command prompt enter this (changing the name (in red) and password in (in green) if you want to):
net user "pmfTurner2" "Password123" /add
net localgroup administrators "pmfTurner2" /add
You can then sign off, sign on as pmfTurner2 user and see if it works... It will say "Getting things ready..." for a while the first time you sign on as the new user - don't worry about that - it is normal..
Do make the USB though - it will the useful if not now then later.