[Nexus 6] Unroot & install OTA update & re-root

INSTRUCTIONS:

# Install ADB and Fastboot tools in your OS
# Download current (YOUR INSTALLED VERSION) factory image from Google Nexus Factory Images
# Extract this archive:
 user@localhost /path/to/download/directory/ $ tar zxvf shamu-{version like: mmb29q}-factory-3bbc7e8b.tgz
# We will get ZIP file called image-shamu-{version like: mmb29q}.zip 
# in /path/to/download/directory/shamu-{version like: mmb29q}/ directory
# Change the directory:
 user@localhost /path/to/download/directory/ $ cd shamu-{version like: mmb29q}
# Extract this archive:
 user@localhost /path/to/download/directory/shamu-{version like: mmb29q}/ $ unzip image-shamu-{version like: mmb29q}.zip  
# All below files was extrated to /path/to/download/directory/shamu-{version like: mmb29q}/ 

userdata.img
system.img
recovery.img
cache.img
boot.img
android-info.txt

# after that run below commands carefully 
 
 adb reboot bootloader
 fastboot flash boot boot.img
 fastboot reboot-bootloader
 fastboot flash recovery recovery.img
 fastboot reboot-bootloader
 fastboot flash system system.img
 fastboot reboot-bootloader
 
# after that reboot device and install OTA Update