- Download the official Android 4.0.3 ICS zip file.
- rename it from ‘VQ8PQk_V.zip‘ to ‘update.zip’.
- Copy/Move the update.zip file to the root directory of the target Nexus S.
- Power off the Nexus S.
- Power back up while holding down the Volume Up button, followed by the Power button.
- Using the Volume keys on the phone, navigate to the RECOVERY option and select using the Power button.
- You should now be seeing an exclamation mark on the screen, don’t be alarmed this is normal. Now hold down the Power button followed by the Volume up button.
- You will now be into your Nexus S recovery menu. Select the update from SD card option, select the ‘update.zip’ file you placedon the phone, press the Power button to confirm the selected update.
- Once you’re done, select the ‘reboot system now’ option and you’ll boot into Android 4.0.3 Ice Cream Sandwich.