You need to have unlocked bootloader it can be done here:
Unlocking the boot loader | Sony Xperia
To install the flash tool, follow the steps below:
Download the Flash tool for Xperia devices.
http://dl-developer.sonymobile.com/t...r_Xperia_3.zip
Unzip the file you downloaded and place it somewhere on your computer.
In the unzipped folder, run Emma.exe. During the installation, make sure you remember the installation path:
Default path in Windows 64 bit is: C:\Program Files (x86)\Sony Mobile\Emma\
Default path in Windows 32 bit is: C:\Program Files\Sony Mobile\Emma\
Copy the Customization.ini file. You find it in the Flash_tool_for_Xperia_X.zip.
Paste the Customization.ini file into the installation folder. The installation folder is the folder named Emma in the installation path examples on point 3.1 and 3.2 above.
Click Start > All programs > Sony Mobile > Emma (if you used the default installation path from step 3 above) to start the flash tool
When you have installed the flash tool for Xperia, you can flash standard Sony software on your unlocked Xperia device. Note! When you flash software onto your device, your user data and content will be erased. Make sure to properly back up all information.
This is how you flash software on your phone:
1. Computer: Open Emma from the Start menu of your computer.
2. Connect a USB cable to your computer.
3. Phone: Turn off your phone.
4. Connect your phone to the USB cable while holding the flash key (for example Volume down). The flash key varies between models. For a complete key mapping, see the list in the bottom of this thread.
Screenshot showing the flash tool when a phone is connected.
5. Computer: Select the software you want to flash in the Service list. The tool automatically detects the phone model and lists available software versions, which are called Services in this flash tool.
6. Click on Apply Service. The phone will now be flashed.
7. Phone: When you have flashed your device, you can disconnect your phone from the computer. The first time you start your device after you have flashed it, the boot-up might take a little longer than normal.
Xperia Tablet Z (SGP321 and SGP311) volume down
Xperia go (ST27i) back
Xperia neo V (MT11i) volume down
Xperia ray (ST18i) volume down
Xperia P (LT22i) volume down
Xperia ZL (C6503) volume down
Xperia Z (C6603) volume down
Xperia PLAY (R800i) back
Xperia E dual (C1605) volume down
Xperia E (C1505) volume down
Xperia T (LT30p) volume down
Xperia S (LT26i) volume down
Xperia arc (LT15i) back
Xperia arc S (LT18i) back