For a while, as part of Sony’s Open Devices program, we have provided a Flash Tool software for developers to flash Sony software to their unlocked Xperia devices. This is useful if you’ve for example flashed a custom ROM on your device, and want to change back to a standard Sony software.
Based on the community request we have now updated the Flash Tool with a new feature, which means that you no longer need to do a complete Software Update if you just want to update the Firmware. The benefit of this is that just updating the Firmware will not erase your Custom ROM, user data nor the device content. Note that performing a complete Software Update will, however, still erase all your user data and content. So, in this case, please make sure to properly back up all information.