How to Update Galaxy S3 GT-i9300 to Unofficially CM13 Marshmallow AOSP ROM.

This is unofficial Marshmallow update for Galaxy S3 as it’s not from Samsung, but is based on Marshmallow code in AOSP source. But if you love latest OS, you’ll love them even though they aren’t as stable as Samsung updates. On the plus side, you get to experience pure Android UI on Marshmallow, as designed by Google.

÷ Prerequisites:

•Samsung Galaxy S3, model no. GT-i9300

•Don’t try this on Galaxy S3 from Sprint, T-Mobile, AT&T, US Cellular and Verizon.

•Don’t try this on any device whose model no. is not same as the one specified above.

•Warranty may be void of your device if you follow the procedures given on this page. You only are responsible for your device.

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*Disclaimer:

Android Custom ROM fix ® provide various Firmware Updates and Rooting process along with Custom ROM,Modes,file are all belong  to their owners/developers. The autor of this site or the developers are not responsible,  if you damage or brick your device.Do it on your own risk and follow the instruction properly.

÷ How to Update Galaxy S3 GT-i9300 to Unofficially CM13 Marshmallow AOSP ROM.

Download Marshmallow AOSP ROM & Marshmallow Gapps for your Galaxy S3.


Step 1. Also make sure that you have installed a custom recovery like TWRP on your device. TWRP recovery is required to be able to install CM13 ROM.


Step 2. Download the AOSP ROM and Gapps file from above.

Step 3. Connect your device to PC and transfer the ROM and gapps file to it. Disconnect the device then. Remember the location of the files on device.

Step 4. Boot your Galaxy S3 into recovery mode. If you are rooted, you can use Quick Boot app from play store. To manually boot into recovery mode, do this:

Power off the device. Wait for 4-5 seconds after screen goes off.Press and hold Volume Up + Home + Power button together until you see anything on screen. Then let go of the buttons.

You will enter recovery mode soon, and should see TWRP recovery. If you see android with exclamation mark, or 3e recovery, then you need to install TWRP recovery for this.

Step 5. [Optional] Once in TWRP, create abackup of your device. Tap on Backup, and then select all the partitions for back. Now do the swipe action at bottom to start creating a backup for emergency cases. This backup is really a lifesaver!

Step 6. Do a Factory Reset. On TWRP’s main screen, tap on Wipe, and then do the Swipe action bottom to confirm it.

Step 7. Now, install the ROM file. On TWRP’s homescreen, tap on Install, and then locate the ROM file and tap on it. Then do the Swipe action at bottom to begin flashing the update.

Step 8. Tap on Home button to go back. Now, install the Gapps the same way you installed Marshmallow ROM on your Galaxy S3.

Step 9. When it’s done, tap on Reboot system button to restart the device.

That’s it.