Based on officialAndroid 6.0 Marshmallow, you can now try the official CM13 Nightly custom ROM on yourSamsung Galaxy S3. Bringing all the usual CyanogenMod features, you can now update Galaxy S3 I9300 to Android 6.0 Marshmallow.

-Android Marshmallow Custom ROMs for All the Android Devices

Prerequisites to update Galaxy S3 I9300 to Android 6 CM13:

Backup any important datafrom your Samsung Galaxy S3 I9300as a complete wipe will be required during the flashing process.Enable USB debugging option on your device:Settings>DevelopmentOptions>USB debugging.Samsung Galaxy S3 I9300 must berooted, unlocked and installed with a recovery tool likeTWRPorCWM.Your device must be charged to at least 60% of power.

Note:this tutorial is focused on Samsung Galaxy S3 I9300; please do not try this guide on otherAndroid&Samsungdevices.

How to update Galaxy S3 I9300 toCM13 Android 6.0 Marshmallow:

Required files: downloadCyanogenMod 13 Android 6.0Nightly custom firmware for Galaxy S3 I9300 and save it on your computer. Do not extract the contents.

Connect your GalaxyS3 to your computer using a USB cable and copy the zip file to your phone’s SD card.Disconnect the USB cord andpower off yourGalaxy S3.Boot it intorecovery modebypressing and holdingVolume Up+Home+Powerbuttons together.Perform aNandroid backupof your current OS:Backup >backupand restoreon ClockworkMod recovery.Wipe data task: from the CWM recovery menu, selectwipe data / factory resetand confirm the process. Then go on towipe cache partitionandwipe dalvik cache.From recovery menu, selectinstall zip fromsdcard,followed bychoose zip from sdcard.Locate the CM13 Android 6.0 Marshmallow custom firmware and confirm the flashing process.Return back to main recovery menu and reboot your Samsung Galaxy S3 I9300 into the new custom ROM. First bootmay take a few longminutes.

How to restore:If you want to return to previous OS on your SGS3, boot intorecovery, selectbackup and restorethen restore yourprevious ROMby selecting it from the list.