Hard Reset SONY Xperia C3 Dual D2502

First method:

1. Switch off the cell phone by holding down the Power button. 
2. Afterwards go to Settings and then to Backup & reset.
3. Then selec Factory Data Reset and tap Reset Phone. 
4. Choose Erase Everything if you are sure you want to clear all your data. 
5. Select OK to confirm the whole operation.
6. Well done!

Second method:

1. First of all, turn off the device by holding the Power button.
2. Afterwards hold down the Volume Up and Volume Down button for a couple of seconds.
3. While holding these buttons press the Power button for a short while.
4. Release held keys when you see an Andoid image.
5. Then press the Camera button to enter Recovery Mode.
6. Choose "wipe data/factory reset" by using Volume Down to navigate and Power button to confirm.
7. Select "Yes--delete all user data". Use Volume buttons button to scroll and Power key to select.
8. To restart the phone, select "reboot system now".
9. Success! The hard reset is done!

Third method:

1. First you should download 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. Now turn your device off.
   
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!

Fourth 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. Next 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. Done!

Fifth method:

1. If the display is off, press the Power to turn it back on.
   
2. Now press Call button, and type: *#*#7378423#*#*
3. Then you will see menu.
4. From this menu choose option Customization Settings -> Reset customization.
5. Confirm information: "data will be cleared and factory data reset will perform".
6. Accept by pressing Reset customization and reboot.
7. Well done!

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