How to Unroot Samsung Galaxy Nexus I9250 to Stock Android 4.1.2 Jelly Bean:

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1. Download the Galaxy Nexus Unroot zip file from HERE. Save the zip on your PC and then extract its contents where the Fastboot folder is located. NOTE: You can find it in the Android SDK/ Platform Tools directory. After you’ve extracted the zip contents you should get to the next step.
2. Power off your smartphone.
3. Boot it into Fastboot Mode by pressing Volume Up, Volume Down and Power buttons, all at the same time. When the display powers ON you should release the buttons.
4. Now, connect your smartphone to your PC using the USB cable.
5. Go to the ‘Fastboot’ folder where you’ve place the ‘unrooting’ extracted files. Press SHIFT key and at the same time right-click the folder’s white space. Select ‘open command window here’ from the context menu. The Windows Command Prompt launches and you have to continue the unroot.
6. Enter the following command to see if your phone has been recognized by the PC: fastboot devices
7. Next, enter the following command lines in order to unroot the device:
   > fastboot flash bootloader bootloader-maguro-primelc03.img
   > fastboot reboot-bootloader
   > fastboot flash radio radio-maguro-i9250xxlf1.img
   > fastboot reboot-bootloader
   > fastboot -w update image-yakju-jzo54k.zip
8. The Galaxy Nexus will restart now and you should be presented with the Android 4.1.2 Welcome Screen.
9. Setup the device and take control over it. These were all the steps you had to take in order to unroot your device.

NOTE: If you want to relock the bootloader also, then you have to follow the steps below:

1. Power off the Galaxy Nexus.
2. Boot it into Fastboot mode.
3. Connect it to your computer using the USB cable.
4. Now, launch again a Command Prompt window on your PC, just like you did at step 5 of the above guide.
5. Enter this command to see that the phone has been recognized by the PC: fastboot devices
6. In order to re-lock the Bootloader of your Galaxy Nexus enter this: fastboot oem lock
7. That’s it, you’ve managed to re-lock its bootloader and you’re done with this tutorial.

If you cannot complete these guides, then you should ask for more help in comments.

refer link : http://www.android.gs/unroot-restore-samsung-galaxy-nexus-i9250-to-stock-android-4-1-2-jelly-bean/