How To Flash a Firmware Using Flashtool

Instructions:

    Switch off your phone and put it aside.
    Extract the “FlashTool_x.x.x.x.exe” file on your PC (you can just double click on it to extract)
    Few files and folders will be extracted — the two which we’ll be using are the ‘drivers‘ folder and the ‘firmwares‘ folder.
    Inside the ‘drivers‘ folder there’s a file named “ggsetup-2.2.0.10.exe”, double click on this file to install the proper driver on your PC.
    Now copy the “.ftf” firmware file that you downloaded for your phone, and paste it inside the “firmwares” folder.
    Double click the “X10FlashTool.exe” file.
    Once the program opens — click on the “Flash” button.
    You’ll see the firmware that you copied in Step 5 loaded on the screen — click “Ok”!
    Now it should ask you to connect your phone to the PC. So first plug the USB cable to PC, then pick up your phone and hold the “Back” key (key at the bottom left on your Arc), and then connect the USB cable to your phone. Remember you’ve to hold the “Back” key while connecting the USB cable to phone.
    Once the phone gets connected — Flashtool will automatically start the flashing process.
    Keep an eye on the Flashtool’s screen.
    And once the process gets finished, disconnect your phone from PC and switch it ON.
    Don’t freak if it takes longer to boot (that’s normal)  as the phone has to build the cache again after flashing.

Flashtool Beta version 0.2.9.1 — Download link. [Source]