In the expectation of an official update for the Galaxy S3 to Android 4.1.2, developers from Root Box and XDA have come up with a stable custom ROM that will allow you to play with the new Jelly Bean.Before proceeding with the update process you will have to accomplish some requirements:- First check the model version of your phone and make sure it is GT-I9300. You can do this by going to Settings, About Phone, Model Number.- Because there are always risks when installing custom ROMs, you should backup your personal data.- In order to install Android 4.1.2 Custom ROM you will need a rooted Galaxy S3. If your device is not rooted, you can check our tutorial about how to root your Galaxy S3.- The next step is to download ROM Manager from Play Store.- Now go to Settings, Applications, Development and look for the USB Debugging check-box and check it.- Free up at least 1GB of space on the SD card- One last thing. Installing custom ROMs on your device and rooting it are actions that present certain risks regarding the functionality of the phone. The device could get bricked and we want you to know that you will do it on your own risk.How to update Galaxy S3 to Android 4.1.2?Step1: Download the Custom Rom that Root Box developed for the I9300.Step2: Download the Google Apps package.Step3: Now connect the device to the USB port and copy the two downloaded files on the root folder on the SD card.Step4: Unplug the device and turn it off. Enter Recovery Mode ( Hold Volume Up, Home and Power until it enters recovery mode).Step5: While in Recovery Mode press <Wipe data/factory reset> and < Wipe Cache partition>.Step6: Now press <install zip from sdcard> and select <choose zip from sdcard>. Look for the custom ROM you downloaded earlier and the Google Apps package and select them.Step7: You have to wait a few minutes for the updates to install. Press<Go back> and <Reboot System now>. This should restart the device in normal mode. Don't worry if it takes longer than usual to reboot.Important: If the device gets stuck at any point, just restart the phone by pulling the battery and start all over again.You now have Android 4.1.2 Custom Root Box Rom installed and ready to roll.

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Update Samsung Galaxy S3 I9300 to Android 4.1.2 with Root Box ROM

What's my model number?

There are several ways to locate your model number:

Option 1
On your device, go to Settings, then "About device" and scroll down to "Model number"
Option 2
Often times you can view the model number inside the device, by removing the battery
Option 3
Using Samsung's model/serial number location tool

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