[jQuery] Change the date format of jquery calendar

Hi all i have one jquery calendar
$('selector').datePicker(); which is giving me in dd/mm/yyyy
i want to change this format to yyyy-mm-dd
i tried with
$.datePicker.setDateFormat('ymd','-');
error: $.datePicker is undefined
and tried with this code
$("#sd").datepicker.setDateFormat('ymd','-');
error: $("#sd").datepicker.setDateFormat is not a function