Before you try the factory reset or hard reset on your device, make sure that you have backup your important files. Restoring the default settings or factory reset your device will delete all your existing files and will go back to its initial state.
>>> On your Home screen, tap Apps.
>>> Go to Settings, and select Backup & reset.
>>> Tap on Factory data reset.
>>> Then Reset phone.
>>> Confirm by tapping Erase everything. You just need to wait while your phone deleting your files and restoring your settings to default.
>>> Download Flashtool from Sony website: http://developer.sonymobile.com/services/flash-tool/
>>> Make sure that the drivers for your USB data cable is properly installed.
>>> Now turn your device off.
>>> Press and hold Volume Down, and connect to USB cable.
>>> Follow the instructions on your screen, and accept appropriate options.
The instruction provided is the general steps on how to Hard Reset and Factory Reset.If the instruction will not work, please make a comment and we will immediately find the correct procedure. Thanks.