(function ($) {
  Drupal.behaviors.change_form_fields = {
    attach: function(context, settings) {
      $('div.form-item-payment-method input').each(function() {
        if (this.value != 'existing-bill') {
          $('div#' + this.value).css('display', 'none');
        }
      });

      $('div.form-item-payment-method input').change(function() {
        show_class = this.value;
        $('div.form-item-payment-method input').each(function() {
          if (this.value != show_class) {
            $('input#edit-' + this.value).val('');
            $('div#' + this.value).css('display', 'none');
          } else {
            $('div#' + this.value).css('display', 'block');
          }
        });
      });
    }
  }
}(jQuery));

$("input[type=radio][name=groupname]").change(function(){

     //Code the clear the form fields or other logic here.
});