How to Hide or remove the WordPress Upgrade Message in the Dashboard

It is very important to keep up to date your WordPress because of security threats, specially now a days due to its popularity. Although WordPress function pop you up all the time for new update version to automatically update it or through providing download link at the top of WordPress admin panel, as well  a link on the update page where you can automatically install the new available version. In case, you are using WordPress for your client or have made lots of customizations on core WordPress files, then might not want this message to displayed, because it will overwrite all the files and client site will lost all the changes. So there are few option to hide it from dashboard through some function adding in function.php file, by using  WordPress plugin to hide this message and manually removing the code from WordPress core file. Different bloggers had provided the solution on their bog like like as follow:

1. Just Open functions.php file from wordpres theme and put following code in that file: (from wordpressapi)

add_action('admin_menu','hide_update_message');
function hide_update_message()
{
remove_action( 'admin_notices', 'update_nag', 3 );
remove_filter( 'update_footer', 'core_update_footer' );
}

2. All you have to do is simply open the theme’s functions.php file and add this: (wpbeginner)

add_action('admin_menu','wphidenag');
function wphidenag() {
remove_action( 'admin_notices', 'update_nag', 3 );
}

3. To get rid of the "Please update now" message in your WordPress dashboard, simply paste the following code on your functions.php file. (wprecipes)

if ( !current_user_can( 'edit_users' ) ) {
  add_action( 'init', create_function( '$a', "remove_action( 'init', 'wp_version_check' );" ), 2 );
  add_filter( 'pre_option_update_core', create_function( '$a', "return null;" ) );
}

4. You can optionally put this code with a condition so that the update message will only be shown to the site admin or other user roles depending of the if-statement in the code snippet below. (fredrikmalmgren)

function hideUpdateNag() {
    remove_action( 'admin_notices', 'update_nag', 3 );
}
if ( !current_user_can('activate_plugins') ) {
    add_action('admin_menu','hideUpdateNag');
}

5. Removing the update message is very straightforward to do – simply add the following lines of code to your functions.php file:(vooshthemes)

remove_action('wp_version_check', 'wp_version_check');
remove_action('admin_init', '_maybe_update_core');
add_filter('pre_transient_update_core', create_function( '$a', "return null;"));

All the above almost do the same thing, If still not satisfied requirments you can use WordPress Plugin to hide "WordPress Upgrade Message" from users and clients dashboard.

Hide Update Reminder

This plugin allows you to hide the update WordPress reminder from all users that are not assumed Administrators (cannot upgrade plugins). If you have multiple users then this means those who are not admins don't need to see the message. Useful for CMS based sites, so the client doesn't see the notice. Detail If you want to display notifications to your user when you update something or when you wish to make an announcement. The plugin "WP update notifier" is simple yet effective and extremely usefull.

Disable WordPress Core Update

Completely disables the core update checking system in WordPress. The plugin prevents WordPress from checking for updates, and prevents any notifications from being displayed in the admin area. Ideal for administrators of multiple WordPress installations . Detail