Hard Reset SONY Xperia M4 Aqua E2303

First method:

1. Start by truning off the cell phone by holding the Power key.
2. From the Main Screen go to Settings.
3. In the next step select option Backup & Reset.
4. Afterwards tap Factory Data Reset and then Reset Phone. 
5. Choose Erase Everything if you are sure you want to clear all your data. 
6. Select OK to begin the process.
7. Well done! The hard reset has just been performed.

Second method:

1. Start by downloading 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!

Third method:

1. First, you should download PC Companion, in example from here:http://www.sonymobile.com/gb/tools/pc-companion/
2. Install it and run.
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

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