Remove the selected options : 
-----------------------------
$('#mySelect2').val(null).trigger('change');

============================================

Completly remove the select2 initialization :
--------------------------------------------
$('#payment_method').html('').select2({data: [{id: '', text: ''}]});

<select id="lang" >
   <option value="1">php</option>
   <option value="2">asp</option>
   <option value="3">java</option>
</select>

<script>
	$("#lang").select2().select2('val','1');
</script>

$('#mySelect').select2({
  data: ['one','two'],
  tags: true
});
$('#mySelect').val(['one','two']).trigger('change')

$('#mySelect2').val('1'); // Select the option with a value of '1'
$('#mySelect2').trigger('change'); // Notify any JS components that the value changed

$('#inputID').select2('data', {id: 100, a_key: 'Lorem Ipsum'});

$('#all_contacts').select2('data', {id: '123', text: 'res_data.primary_email'});