I have a datpicker and i want to change the Format. i know that i have to use the formatDate function, but where do i put it?

<script>

$.datepicker.formatDate( "yy-mm-dd", new Date( 2007, 1 - 1, 26 ) );

  

  $(function() {

    $( ".datepicker" ).datepicker();

    $( ".selector" ).datepicker({ dateFormat: "yy-mm-dd" });

  });

     

  </script>