Every android users are waiting for the latest update of Android 4.1.1 Jelly Bean in their devices, however, few lucky ones who can enjoy it in the short term, as very few manufacturers have announced that they have available for their devices.
Google have promised to upgrade their devices to Android 4.1, from the Nexus S on. But this update has not yet officially arrived, however, the guys at XDA Developers have managed to port Android to Google Jelly Bean Nexus S still waiting for the official update.
Although this is an unofficial ROM, users who have tried it seem to be fairly comfortable, because it is a fully functional firmware.
Before we start the tutorial about How to Upgrade Google Nexus S to Android 4.1.1 Jelly Bean, Please note that :
Disclaimer: This process may brick your device. We do not take any responsibility for anything you do to your device.
Tutorial HOW to UPDATE NEXUS S to ANDROID 4.1.1 JELLY BEAN
1. Download the ROM of Android 4.1 from this link
2. Connect the Nexus S to the PC and place the update.zip package within the device's SD card.
3.Then disconnect the device, you have to turn it off to enter the recovery mode. To do this you have to keep pusaldos the volume down buttons and lit at once. If the device boots in normal mode, you can try again.
4. Since the recovery mode, select Wipe data / factory reset and Wipe Cache partition. Then you have to restart the device by selecting reboot system, for which you can use the volume keys up and down.
5. Re-enter recovery mode and select install zip from sd card> choose zip from sd card and then choose the package Jellybean Android 4.1 and select "Yes" with the help of the volume control buttons and the button Menu.
6. After selecting the file, the update process began. After 4 or 5 minutes, you have to click on "Go Back" and choose "reboot system now"
7. Ready! You've updated to Android 4.1 Nexus Jelly Bean.
Note : If at any time the firmware update process is stopped for any reason, all you have to do is restart the process from the beginning re-inserting the battery.
Credit to legolas93 from xdadevelopers forum