I have 10.3.3 downloaded to win10 28gig laptop
I cant work out how to update this to iphone6
(...)
There must be a solution of downgrade whilst making use of 10.3.3 file direct from win10 desktop
hold the "Shift" key and select previously downloaded 10.3.3 ipsw file:
http://osxdaily.com/2010/11/23/how-to-use-ipsw-files/
Cheers,
Matt