If you’re using the HTC One M7, the latest Android 4.4.3 KitKat is rolling out now via OTA (Over the Air) update. The upgrade for last year’s flagship is quite quick considering its current One M8 was just updated several weeks ago.
With the file size of 605MB, it is advisable to download this using WiFi. If you haven’t gotten any notification yet, you can try checking manually under Settings > About > Software. Apart of having the latest Android 4.4.3 with security fixes, the new software update with the version number 6.13.707.1 also updates the Camera, Gallery and HTC Sync Manager.