Now Android latest version is Android O now you can
update by receiving OTA.
I will tell you how to install Android O simply by receiving OTAupdate.
This update will only work on Nexus 5x, Nexus 6P, Nexus Player, Google Pixel C, Google Pixel, Google Pixel Xl. Otherwise you have to wait.
This is very process but it is not stable yet you will se some bugs, battery life, connectivity so you have to care about this things.
How to install Android O-
Firstly open your browser and type andriod.com/beta it is very simple step then you have to sign in with your gmail when you will login then a page will open where you can see Android Beta Program then when you scroll down you will get to see that your phone is eligible or not if you are eligible then you click that button and one page will open again there you can read all the warnings and after accepting the terms and condition click to join beta after then you will simply get the OTA update if you want to go back to nougat simply go to the same site and follow the steps but your all data will go.And lastly you will get one option in notification panel click on that you will see one download option and your download will start, Android O is 919 Mb.