Why Windows 10 shows a notification to install latest version ?

If you are currently using windows 10 version including 15017 , 1511 or version 1607 0r 1703 then there are chances that you might get the notification to install the latest version of windows
to get security updates.
When you receive the update notification, click on Update Now  to update your version.
1709(latest version)
Version 1507 and version 1511 are currently at the "end of service" and may no loner receive the monthly security updates and to get the updates you have to install this latest version which is shown in the notification i.e 

To ensure things go smoothly:

- Keep your PC plugged in.
- Don't turn your PC off or close it.

ALSO CHECK : What is KB4088776 update for windows 10?