Hard Reset SONY Xperia Z4

First method:

1. Start by turning on the device by holding the Power key for a short while.
2. In the next step find and select Settings and tap Backup & Reset.
3. Afterwards tap Factory Data Reset and then Reset Phone. 
4. Choose Erase Everything if you are sure you want to clear all your data. 
5. Next, select OK to confirm the whole operation.
6. Well done! The hard reset has just been performed.

Seconds method:

1. First of all, you should download PC Companion, in example from here:http://www.sonymobile.com/gb/tools/pc-companion/
2. Next, install and run this application.
3. Then you will see window with 4 options.
   
4. Choose option "Support Zone New!", and click "Start".
   
5. Wait for the program to install the appropriate add-on.
6. After that you will see next window with 3 options.
   
7. Go to option "Phone / Tablet Software Update", and click "Start".
8. Select "repair my phone / tablet".
   
9. Now follow the instructions and accept all informations. 
   
   
10. Please be patient and wait until preparing computer for software update is complete.
    
11. Afterwards choose your phone / tablet model.
    
12. If you see this window, then connect your device into your PC.
    
13. That's all

Third method:

1. At first, download the flashtool from Sony website:http://developer.sonymobile.com/services/flash-tool/
2. Make sure, that you have installed drivers for your USB data cable.
3. After that, power off your device
   
4. Then press and hold Volume Down, and connect to USB cable.
   
5. Follow the instructions on your screen, and accept appropriate options.
6. Success! Your phone is ready to use.

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