Hard Reset SONY Xperia Tablet Z WiFi

First method:

1. Switch off the tablet.
   
2. Now navigate to Settings -> Backup & reset -> Factory Data Reset -> Reset tablet.
3. Then choose option option "Erase everything", and confirm that.
4. Success!

Second method:

1. You should first download and install program PC Companion.
   * In example from here: http://www.sonymobile.com/gb/tools/pc-companion/
2. If all went well, you will see window with 4 options.
   
3. Next click "Start" under the name "Support Zone New!".
   
4. Wait until the process of the installation is completed.
5. Now you should see window with in example option "Phone / Tablet Software Update".
   
6. Accept this option -> click "start".
7. Then click "repair my phone / tablet".
   
8. Please follow all instructions, and confirm that.
   
9. Read "Inportant information", and confirm.
   
10. Afterwards PC Companion is "preparing computer for software update".
    
11. Next select your phone / tablet model.
    
12. Follow steps, which you see in new window.
    
13. That's all!

WARNING !
Hard Reset will erase all of your data
All described operations you are doing at your own risk.