I have an "ancient" Windows Phone 7.0, later upgraded to 7.5. Now I had to return to "Factory Settings" which brought me back to 7.0. Is it possible to get somewhere the 7.0 to 7.5 5 upgrade pack? Thanks
You'll need the Zune Software for updating WP7 phones - I think you can still get it here. When you connect your phone it should offer you to download the necessary packages and update your phone - if Microsoft hasn't disabled this yet.
I used this back in the day on my Lumia 710. Dunno if it'll help you.