The Sony Xperia M was first introduced to an unsuspecting world last year, where it arrived with Android 4.1 Jelly Bean in tow.
Now, this mid-range smartphone is on its way to receive an operating system update which will bump up the version number to Android 4.3 Jelly Bean.
Do bear in mind that this particular update seems to affect only the single-SIM Xperia M device, and it does not seem as though the dual-SIM model has started to receive this particular update.
Apart from that, one ought to take note that the update does seem to have been released for some carrier versions of the Xperia M in Europe and Asia, and not for the unlocked and SIM-free devices. It might take some time prior to your Xperia M handset receiving this update, so do be patient if it does not seem as though anything has happened.