Jon Cave

If you don’t check your admin panel on your WordPress install very often (maybe because you prefer to use remote publishing) or you want to make sure 
that your clients’ WordPress installations are updated, then this is the plugin for you. You don’t have to login to your admin panel regularly, 
suscribe to an RSS feed, or do anything apart from installing this plugin to be notified when an update to WordPress is released.
All you have to do is install Update Notifier and forget it until you receive an email telling you to update.
To change Update Notifier’s options, go to Update Notifier under the main Settings menu. From there you can add a secondary email address 
which will also receive update notifications and you can activate update notifications for themes and plugins.

Update Notifier

Sends email notifications if a new version of WordPress available. Notifications about updates for plugins and themes can also be sent.

Scott Reilly

This plugin removes the WordPress update nag that appears at the top of all admin pages when a new version of WordPress is released.
Tired of WordPress nagging you about a new release? Maybe you already know about it and want to hold off on an update and would rather not see the update nag on every admin page you visit. Activate this plugin and be bothered no more!
The status of your version of WordPress (be it current or out-of-date) is still reflected in the footer of your admin pages and in the update count link in the admin bar.
And certainly, of course, I don’t advocate completely ignoring the fact that updates often contain fixes for critical bugs or exploits. However, there are various other means of learning about updates; and once known, not everyone is able or willing to update immediately.
Links: <a href="https://coffee2code.com/wp-plugins/no-update-nag" rel="nofollow ugc">Plugin Homepage</a> | <a href="https://wordpress.org/plugins/no-update-nag/" rel="ugc">Plugin Directory Page</a> | <a href="https://github.com/coffee2code/no-update-nag/" rel="nofollow ugc">GitHub</a> | <a href="https://coffee2code.com" rel="nofollow ugc">Author Homepage</a>

No Update Nag

does what it says on the tin

Removes the WordPress update nag that appears at the top of all admin pages when a new version of WordPress is released.

Update Notifier vs No Update Nag