The Samsung Galaxy S3 is pretty old now but there are some people out there that are still holding on to it. If you are one of them and would like to try out the new Android 7.1, here is how you can do it on your own.
Bear in mind that the build might be missing a few important CM features but the developers are saying that they will work to add in more with time. With the ROM, Samsung Galaxy S3 users will be able to use some of the new features like protected app, LiveDisplay, Privacy Guard and more.
Make sure you backup all your important data before starting. Start by installing the CM14.1 Nougat ROM here as well as the Gapps. Now, turn off the device and enter Recovery Mode. Created a Nandroid backup using TWRP and do a Factory Reset.
Next, locate the ROM zip file and install the ROM. Once that is done, flash the Gapps. Finally, wipe cache & Dalvik cache once more and reboot the device. Your device should be running on the Android 7.1 OS now.
The ROM will only work on the Samsung Galaxy S3.