need help with iPhone 4s

Okay I’m new here, what I want to do is take my old iPhone 4s back to an OS that supported Camera Roll. My girlfriend “updated” my phone and not only has the latest iOS but she deleted over 7,000 pictures I had in folders. I tried to retrieve them but they are all in All Photos plus some are in there twice because I have over 8,100 now. Plus, I lost some 700 songs I had loaded onto my iPhone from my CD collection. What I need to know is which iOS do I need and how do I go about it? BTW I had backed up my iPhone to a Windows 7 based laptop but I had to format the HD and reinstall the drivers. I never got around to backing up my phone before she decided to help me. I need help plz.

thanks all. Blair