Here is a guide to show you how to flash a FTF file to Sony android phones, in this instance we flashing to a Sony Ericsson Xperia Play using Bin4ry & Androxyde's Flashtool
Here is a guide on how to flash a FTF (official firmware) to the Xperia Play using Flashtool. You do not need to have a modified or unlocked phone for this to work for you.