Have Win7, can't install on Late 2013 iMac (Upgrade to 10?)

Ok, I have a Late 2013 iMac and a legal full copy of Windows 7. Now I know that I can't do an install of Windows 7 with this machine in bootcamp as there are no default USB3 drivers in Win7 and I have no keyboard/mouse available to finish the install (fought this battle a year ago so unless you're brilliant and know how to get around it I'm screwed on that point).

That said, I have a legal copy of Windows 7, thus I should qualify for Windows 10, which WILL have support for an install on my iMac. But how the hell do I claim the upgrade? I don't have windows updater to install it or claim it?

Any help would be appreciated. Thanks!

 

Why don't the mouse/keyboard work then? (Honest question)

 

I've tried several. most basic of which is a microsoft USB keyboard. It's about 8 years old, it's worked without drivers on literally every system I've ever used.

Also another thing. I had a 2011 iMac prior to this 2013 and it installed with the exact same hardware and software with zero issues.