Remember that if you already have the previous version of CM12.1 ROM running on your phone, then all you need to do just launch the System Update feature through your phone. But if you haven't flashed it before then you can prepare everything needed before taking yourself into the full details of the instructions.
And I do expect you have realized that whatever will happen, whether it's good or bad, after flashing the ROM will be your own responsible to bear.
You can use the complete tutorials here to update Sony Xperia Z Ultra To Lollipop (Android 5.1.1 software).
- Have already installed a custom ROM, like CWM or TWRP recovery.
- Have a rooted device.
- Remember that your phone should already bootloader unlocked before getting to the instructions. Read the full guides here to unlock bootloader of Sony devices.
- Enable your Xperia Z Ultra USB debugging mode.
- Create backups to your existing data before starting.
- A computer with a USB cable.
- Gapps will be separately installed.
- Have a sufficient batter power.
- Sony PC will stop detecting your phone once this modified ROM is fully installed.
Perform the flashing instructions here, you are invited not being forced, so the choices are yours. Since you take the invitation then you should know, none should be held responsible for any unwanted results during or after the process of flashing the ROM.So proceed at you own risk. And good luck.
Tutorials to flash the Official CM12.1 ROM on Sony Xperia Z Ultra
Files needed for the installations.
- Download the zip file of the CM 12 ROM from here.
- Download Gapps here (88.02MB).
- Now plug your Xperia Z Ultra to a USB cable then connect it to your computer's USB port. Then transfer all the zip files you downloaded to your phone's internal storage -- I recommend to place them to root folder in your phone.
- Now unplug your phone from computer when the files transferring finished.
- Completely power off your phone to further entering recovery mode.
- When your phone in the recovery mode choose the Wipe Data/Factory Reset.
- Now choose Wipe Cache Partition when done, go to Advanced menu to perform the Wipe Dalvik Cache.
- You can now choose the Install Zip From SD Card to further selecting the Choose Zip From SD Card and then flash the ROM zip file.
- You can flash the Gapps zip file using the same method above.
- Now *****Go Back***** and when you are on the main menu reboot your phone with the Reboot System Now option.
- You did it.