How to enable automatic updates

Add the following code to your WordPress installation’s wp-config.php:

/* Enable automatic updates */
define( 'WP_AUTO_UPDATE_CORE', true );
add_filter( 'auto_update_plugin', '__return_true' );
add_filter( 'auto_update_theme', '__return_true' );

Source: https://codex.wordpress.org/Configuring_Automatic_Background_Updates