add_filter( 'wp_nav_menu_items', 'snippetpress_change_my_account_label' ); 
  
function snippetpress_change_my_account_label( $labels ) { 
   if ( ! is_user_logged_in() ) { 
      $labels = str_replace( "My Account", "Log In", $labels ); 
   } 
   return $labels; 
}