I try to update data through ajax, but it not worked. What I did wrong?
Here is jquery ajax code

jQuery('.upd_btn').click(function(){
        // var id = jQuery(this).attr('data-id');
         var form = "#test-form";
        // alert(id);
        $.ajax({
            url: '<?php echo admin_url('admin-ajax.php');?>', // this is the object instantiated in wp_localize_script function
            type: 'POST',
            data: jQuery(form).serialize(),
            //  data:{ 
            action: 'update_records', // this is the function in your functions.php that will be triggered
            // //   update_record : id,

            // },
            success: function( data ){
                alert("Records are successfully update");
                location.reload();
            }
         });
    });

this is update query in functions.php

function update_records(){
  global $wpdb;
  echo $id = $_POST['update_record'];

  // echo'<pre>';print_r($_POST);echo'</pre>';

  $db_updated = $wpdb->update( $wpdb->prefix.'contact_form',  
 $data =array( 
        'names' => $_POST['yourname'], 
        'emails'    => $_POST['customer_email'], 
        'gender' => $_POST['customer_gender'], 
        'age' => $_POST['customer_age'] 
                                ), 
  array( 'ID' => $id ) );
}
add_action( "wp_ajax_update_records", "update_records" );
add_action( "wp_ajax_nopriv_update_records", "update_records" );