How to upgrade the Galaxy S3 I9300 to Android 4.1.1 Jelly Bean

One of the perks of having an Android device is the endless possibilities for you to customize its performance and look. If you are an Android fan, you've probably been through flashing a lot of different custom ROMs to your device but you never find it as a chore. Instead, flashing custom ROMs may seem like an enjoyable thing to do since you can have your device run on a faster, smoother, and prettier OS.

Talking about custom ROMs, CyanogenMod is hands down one of the most popular and most used custom ROMs by many Android users. Developers have also made their own builds based from CyanogenMod. And luckily, the international version of the Samsung Galaxy S3 has been blessed with numerous Jelly Bean-based custom ROMs for the past weeks.

In addition to the custom ROMs made for the Samsung Galaxy S3 GT-I9300, XDA Developers member temasek has released an unofficial Jelly Bean-based CyanogenMod 10 ROM. Some extras are mixed in for better experience with the ROM but still keep in mind that this ROM is still in its early stages so expect some bugs to be present.

In this guide, learn how to upgrade the Galaxy S3 I9300 to Android 4.1.1 Jelly Bean via CyanogenMod 10 (unofficial).

Warning

The instructions in this guide are intended for use with the Samsung Galaxy S3, model number GT-I9300. Applying these instructions on another device or model may produce undesired outcomes.
The information in this guide is provided for instructional and educational purposes only. There is no guarantee that these instructions will work under your specific and unique circumstances.
Use these instructions at your own risk. We shall not hold any responsibility or liability for whatever happens to you or your device arising from your use of the info in this guide.
Read and understand the whole guide first before actually performing the instructions.

Requirements

A Samsung Galaxy S3 with CyanogenMod 9 and ClockworkMod Recovery installed. For help with meeting the mentioned requirements, check our guides:
Download the following files:
- Temasek's unofficial CM10 ROM for the S3 (cm-10-20120816-UNOFFICIAL-i9300-V27.zip, md5sum: 0be50afa9c22371ea866fb37207c6b02).
- GApps (Google Apps) package (gapps-jb-20120726-signed.zip, 83.1 MB)
See to it that your phone's battery is charged up to 75% or more to avoid interruptions during the process.
Backup all personal data on your phone to make sure you have a copy of your personal data (e.g., contacts, SMS, MMS, Internet settings, Wi-Fi passwords, and the like) in case the procedure in this guide erases such data.
- For backup tips, check our guides on how to sync your data to the cloud and how to create local backups of your mobile data.

Instructions

Copy the CM10 ROM and the GApps (Google Apps) package to your phone's internal SD card.
Switch your phone off and boot into ClockworkMod Recovery. To do this, press and hold the Volume Up, Home, and Power buttons together until recovery boots.
- NOTE: While in recovery, you can use the Volume keys to scroll up or down and the Power button to select an option.
Make a NANDroid backup of your existing ROM in case of problems with this ROM. To create a backup, go to Backup and Restore and select Backup.
Wipe the data on your mobile phone (you may skip this step if you came from a previous version of this ROM):
- Select Wipe data/factory reset and confirm the action on the next screen. Wait until the process is done.
- Go to Mounts and Storage and select Format system.
Select Install ZIP from SD card.
Select Choose ZIP from SD card and navigate to the ROM ZIP file and select it. Confirm the action on the next screen to start installing the ROM to your phone.
After installation of the ROM is done, install the GApps package in the same manner as steps 5 and 6.
Once installation is done, select Go back and select Reboot system now. This will reboot your phone to the newly installed ROM.