Sony has rolled out Android 5.1 Lollipop security update for the Xperia Z1, Xperia Z Ultra and Xperia Z1 Compact. The update brought fix for the Stagefright vulnerability and some other minor improvements including camera and over all user-interface and media. The update is rolling out via OTA and the supported devices can be easily updated to latest firmware using your Sony devices. The OTA update is rolling out in batches and may take some time depending upon the region or carrier to which the device belongs.
The Android 5.1.1 Lollipop firmware update with build number 14.6.A.0.368 is a FTF file and can also be installed with manual procedure using firmware Flashtool, this method would be helpful if you are not getting the OTA notification. The Android 5.1.1 Lollipop firmware is specifically released for the Xperia Z1 C6902 and C6903, Xperia Z1 Compact D5503, and Xperia Z Ultra including variants (C6833 & C6806).
The Android 5.1.1 Lollipop update not only a security update but also contain improved volume control, Calendar and Contacts integration with LinkedIn, enhanced Camera focus and speed and accuracy improvements in Superior Auto mode. In fact the update brought multiple improvements beside firmware update. Just go ahead and check for the OTA by following the below guide.
How to update Sony Xperia Z1, Xperia Z Ultra and Xperia Z1 Compact via OTA (Over-The-Air) method
This is the first and preferably the most easiest method to update your device, you can use your device to download the firmware file if available and then the device will ask you to install the updates now or later. To check whether your device is eligible for OTA Firmware update, unlock your device & navigate to
Settings >> About device >> Software update >> Check for updates
This will require a working internet connection to connect to the Samsung servers. You will receive a notification about the latest firmware availability click install to flash the firmware or tap install later to flash the latest update anytime later.
For manual installation visit Xperia Blog and grab the firmware file and flash it via Flash-tool.