Pre Requirements :-
download Flashtool and install form here.
firmware download link
Run the FlashTool.
click on the flash and choose “Flash Mode”
Then you get into this menu Simply click “D2105” and then on “flash”
Then plug your Xperia moment (Hold volume down – for a while and plug usb cable ) You should have a green light, if everything ok. then Flash tool displays a green bar lets finish up.