Android 5.1.1 Lollipop is now out which means we are seeing some major custom ROMsgetting the update too. You can now update your Samsung Galaxy S3 T999 to Android 5.1.1 based CyanogenMod 12.1 custom firmware. While you won't see the official Android 5.1.1 update coming from T-Mobile, there is no reason why you shouldn't update your phone via the custom means. Follow this guide toupdate Galaxy S3 T999 to CM12.1 Android 5.1.1 Lollipop custom ROM.

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Prerequisites to update Galaxy S3 T999 to CM12.1 Android 5.1.1:

Backup any important datafrom your Samsung Galaxy S3 SGH-T999 as a complete wipe will be required during the flashing process.Enable USB debugging option on your device:Settings>DevelopmentOptions>USB debugging.Samsung Galaxy S3 T999 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 T-Mobile Samsung Galaxy S3 SGH-T999; please do not try this guide on other Android &Samsungdevices.

How to update Galaxy S3 T999 to CM12.1 Android 5.1.1:

Required files: download CyanogenMod 12.1 Android 5.1.1custom firmware for Galaxy S3 fromhereand save it on your computer. Do not extract the contents.

ConnectGalaxyS3 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 into recovery mode bypressing and holdingVolume Up+Home+Powerbuttons together.Perform aNandroid backupof your current OS:Backup>backup and restoreon ClockworkMod recovery.Wipe data task: from CWM recovery menu, selectwipe data / factory resetand confirm the process. Then go on towipe cache partitionandwipe dalvik cache.From recovery menu, selectinstall zip from sdcardfollowed bychoose zip from sdcard.Locate the CM12.1 Android 5.1.1custom firmware and confirm the flashing process.Return back to main recovery menu and reboot your T-Mobile Samsung Galaxy S3 into the new custom ROM. First boot takes a good 5 minutes so please be patient.

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

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