Before you update your Xperia Z, make sure that you fulfil all the requirements needed:
1- Create a backup of all your personal information, settings and data files.
2- Make sure that the battery level must be at least 50 percent.
3- Enable the USB debugging mode( If 1st time and Developer options are not visible go
to settings -- about phone and click on build number 8 clicks ).Then Go to "Settings > Developer options > Enable developer options > USB debugging."
4- Disable the MTP mode on the device. Go to "Settings > Xperia > Connectivity > USB connection mode > Choose MSC."
5- Download the Android 4.2.2 For Xperia Z1 C6903 Jelly Bean packages tft: download .Tft here to your computer.(Ftf file)
6- Download from here the Flashtool to your computer.
7- choose & Install your Usb drivers from from here
1. Install the Flashtool app which you have downloaded earlier to your computer.
2. Connect your Sony Xperia Z1 to your computer using a USB cable.
3. Copy the downloaded "ftf" from the official firmware file to the Flashtool folder -
"C:flashtoolfirmwares" folder on your computer.
4. In the flashtool kit, click the "lightning icon, " select on "flashmode" and then press "ok."
5. Look for the ".ftf" system file on the flashtool folder and select the same one you downloaded.
6. Now select the "flash" button and ''flashmode'' then disconnect usb from xperia z1 and power off device. and keep press down volume and connect a Usb cable to begin updating your device. Be patient since the update will take several minutes.
7. Once the installation has been completed, disconnect the usb from the computer and then reboot it.
...Congratulations! Your Sony Xperia Z1 is now updated and running Android 4.2.2 Jelly Bean OS. If you want to confirm the Android version, go to "Settings > About phone > Android & Baseband versions. This manual update does not require rooting your device and may remove root access once installed.