I have 2 s7 from market but systems are messed up Can someone link me where I can download the Android latest system  os file to download to SD  card so I can reinstall phone os system from phone update boot screen thanks I got 2 x s7 but there got some dodgy apps installed to system that can't be uninstalled cheers
Well, there's 2 things to consider:


it would be simpler to uninstall those troublesome apps. I believe you tried uninstalling those apps as a "regular user." If those apps have been marked as "system apps," you will need "root privileges" to uninstall them. First you will need to "root" your phone, and there are different ways to do that. Once that's done, you can find an app that uninstalls "bloatware" and/or "system apps." That route has always worked for me.
if you really want to reinstall Android to have a clean slate, what you are looking for is called a ROM. There are many out there, and it needs to have been made specifically for your phone. Some are just plain Android, some have a "design philosophy" or a "purpose." Once you figure out how to flash a new ROM, you can go and try different ones until you find one you like.