Step-2: Connect the Xperia Z to the computer via USB cable. Without extracting the zip file, copy the downloaded firmware zip to the root folder on phone's SD card.
Step-3: Disconnect the phone from computer and then Power it off
Step-4: Boot the Xperia Z into recovery mode by pressing and holding Volume Up, Home and Power buttons together. The recovery mode will appear soon.
Note: In recovery mode, use Volume buttons to navigate between options andPower button to select the desired option.
Step-5: In recovery mode first perform a Nandroid backup of the existing ROM which can be restored later if the new ROM does not work or users want to return to the previous firmware. To perform a Nandroid backup, select Backup and Restore then select Backup again on the next screen. When backup is completed return to the main recovery menu.
Step-6: Perform data wiping task to eliminate clash between the new ROM and the previous ROM. Select wipe data/factory reset then select Yes on the next screen to confirm the action. Then select wipe cache partition and after the wiping process completes select Wipe Dalvik Cache under advance option. Once the wiping process is done, go back to the recovery menu.
Step-7: Select Install Zip from SD card then select Choose Zip from SD card. Now locate the Android 4.3 CyanogenMod 10.2 ROM zip which was earlier copied to the phone's SD card. Press the Power button to select it and confirm installation on next screen.
Step-8: Once the installation process is completed, return to the main recovery menu and reboot the phone by choosing reboot system now. The first boot will take some time.
The Xperia Z should now be successfully updated with Android 4.3 CyanogenMod 10.2 ROM. Navigate to Menu>> Settings>> About phone>> Software info to verify the new firmware running on the device.
Note: To go back to the previous ROM, boot the Xperia Z into recovery mode. Then select Backup and Restore and restore the ROM by selecting it from the list.