Nexus S was the second Nexus phone from Google. Manufactured by Samsung, it was the first phone to showcase Gingerbread (Android 2.3) in all its glory. The phone is now two years old. If you’re carrying around this smartphone (still awesome today) then follow the step below to get Android 4.1.2 on your smartphone.
Do note that this is an unofficial firmware. But is CyanogenMod 10, which happens to be the best custom ROM on Android. You will need a Nexus S with a custom recovery installed. As always, back up all your important data and keep your phone fully charged.
Step 1- Download the ROM
Step 2- Connect your phone to a computer using mass storage mode
Step 3- Copy and paste the ROM downloaded in step 1, into the root folder of the mass storage device
Step 4- Turn off your phone and reboot into the bootloader. Do this by pressing and holding the Volume Up + Volume Down and Power buttons.
Step 5. Use volume rocker to navigate and power button to click. Perform a data wipe + cache wipe
Step 6. Navigate to flash ZIP from SD card and choose choose ZIP from SD card
Step 7. Select the ZIP file downloaded in step 1. Select it using the power button and confirm installation.
Step 8. When installation is done, go back to the main menu of CWM and perform a reboot
After that’s done make sure to Download Gapps and install them through CWM.