Android 5.1.1 Lollipop OTA Update, Factory Images For Nexus 10, Nexus 7 Available: Nexus 9 To Get It Soon [How to Install]
Android 5.1.1 Lollipop Update For Nexus 10, Nexus 7: Factory Images, OTA Update AvailableScreenshot from Google's Android Official Site

Google has finally released its much-awaited Android 5.0 Lollipop OTA (Over-The-Air) update to the Nexus 4, Nexus 5, Nexus 7 (2012 & 2013 editions), and Nexus 10 after weeks of anticipation. Google Play Edition devices, including Sony Xperia Z Ultra, Samsung Galaxy S4, HTC One M7, M8, LG G Pad 8.3, and Moto G will also get the software update.

However, it may take some time for the new software to reach some parts of the world, as the update will be rolled out in phases. Owners of Nexus devices and Google Play Edition devices may however check the availability of the firmware through: Settings >> About Device >> System Updates >> Check now

For those who have received the software, here is step-by-step manual tutorial to install it.

Things to do before starting the update:

- Connect your Nexus device to your computer using a USB cable.
- Install Android SDK on your machine with ADB and Fastboot command successfully working. Here is the tutorial.
- 7zip or a similar program that can handle .tgz and .tar files is needed and it can be downloaded for free.
- Get an appropriate factory image for your device and it can be downloaded from the official website.
- Make sure that you get the right factory image for your device.
- Back up personal data like photos as all user data will be deleted after flashing a new system image. [Tutorial to flash a system image

NOTE: It may be mentioned that Google has not provided factory image for Nexus 4, Nexus 7 (2013), and Nexus 7 (Mobile) yet.

Manual tutorial to update Android 5.0 Lollipop on your Nexus device:

- Boot your device into fastboot mode by turning it off and holding down the volume up before pressing power.
- Use 7zip, which is saved in your computer after being downloaded from Android Developer site, to extract the .tgz file. Extract the .tar file extracted from the .tgz. file with 7zip again.
- Copy all the extracted files and paste them on platform-tools folder in the Android SDK on your computer, which should be in C drive, and under Program Files (x86) on Windows.
- Now, connect your device to your PC. ADB and Fastboot commands should be working by this time.
- There are two flash-all files. Double click "Windows Batch File" if you are on Windows, and file if you are on Linux.
- Installation should start by now with a box popping up if all the procedures are correctly followed.
- Do not unplug your device while installation is in progress.
- Your Nexus device will reboot automatically after installation is done, and Android 5.0 Lollipop boot animation will start up.
- You can disconnect your Nexus device from your computer. You have got Android 5.0 Lollipop.