You'll need to install a custom recovery to flash a ROM. Open the Flash tool folder (usually C:\Flashtool).Find folder named Driver. Run the program named "Flashtool-Drivers",check all the options under "select component to install". Click install. Come back to Flashtool folder find folder named "firmwares".Copy downloaded firmware files(.ftf files) to "firmwares" folder.Open flashtool.exe connect the phone using USB cable (in Mass Storage mode). You can find your Phone details at INFO log.Wait until the process complete. When INFO log shows finished , device disconnected , you can switch on your phone . It'll take 10-15 minutes for first boot .