First method:
- Power on the phone.

- Then goto Settings -> Backup & reset -> Factory Data Reset -> Reset Phone.
- Now select option "Erase everything", and confirm that.
- Done!
Second method:
- First you should download flashtool from Sony website: http://developer.sonymobile.com/services/flash-tool/
- Make sure, that you have installed drivers for your USB data cable.
- Now turn off your device.

- Then press and hold Volume Down, and connect to USB cable.

- Next follow the instructions in your screen, and accept appropriate options.
- Success!
Third method:
- Switch off your cell phone.

- Next hold and press Power button + Volume Up for about few seconds.

- Release them, when you see menu on your screen.
- Now follow the instructions on your screen.
Fourth method:
- First you should download PC Companion, in example from here: http://www.sonymobile.com/gb/tools/pc-companion/
- Install it and run.
- Next you will see window with 4 options.

- Choose option "Support Zone New!", and click "Start".

- Wait for the program to install the appropriate add-on.
- After that you will see next window with 3 options.

- Goto option "Phone / Tablet Software Update", and click "Start".
- Select "repair my phone / tablet".

- Now follow the instructions and accept all informations.


- Please be patient and wait until preparing computer for software update is complete.

- Afterwards choose your phone / tablet model.

- If you see this window, then connect your device into your PC.

- Done!