1. You will need a device running on the latest stock Android firmware. You will need an unmodified system. Any modifications like root/SuperSU, custom recovery, unlocked bootloader may fail the installation of the OTA. However, it won’t affect the OTA notification.
2. Enable USB Debugging on your device. To do so, go to Settings > About Phone. Tap on the Build Number several times until you get a new Developer Options in the Settings. Open Developer Options and enable USB Debugging from there. Trust the connection by allowing it when you connect it to your PC for the first time.
3. Make sure you have latest device drivers setup on your PC for a better connection. Get it from the official page of your device manufacturer.
4. Setup ADB and Fastboot environment on your PC.
Step 1: When you get the OTA update notification, do not download the update. Also, and do not reboot your phone.
Step 2: Setup ADB and Fastboot environment on your PC and enable USB debugging on your Android device. (settings>development>enable USB debugging)
Step 3: Now plug in your device to the PC using a USB cable. (not a front port)
Step 4: Now open the command prompt or terminal by holding the shift key on your PC and press the right mouse button. Alternatively, go to start>accessories>cmd or type cmd in the search under the start menu.
Step 5: Now issue the following command in the cmd window:
adb logcat > log.txt
Please take note that the log.txt is dependent on your working CMD directory.
Just open the log.txt and search and copy the .zip file url and you can download it using your browser or download manager.