1. How to Flash Android Sony Xperia Z Ultra C6833
a) First of all, check your firmware version (if you already have the latest, you do not need this tutorial)
b) Download and install the latest Flashtool
c) Download the latest firmware for the Sony XPERIA Z C6833 Ultra Here all sony firmware here
d) Paste FTF file downloaded in step c) to the folder "Firmware" in the folder Flashtool
e) Open Flashtool, click on the flash and select the firmware was downloaded, click ok. Important - if you do not want to delete the data from your phone, simply uncheck userdata.sin. All data will remain in your phone, but sometimes it can cause additional problems. So it is better (and I recommend) to perform a backup of your personal data, continue with the installation clean and then restore your personal data.
f) Turn off your phone and when Flashtool show pop-up window, connect the phone to the PC by pressing the volume down key until the Led green color appears
g) After a few minutes all done and you get new firmware phone
This is Full Tutorial : How To Flashing Sony Xperia Via Flashtool
