Change the Text of a Option with jQuery

Answer 1

$('select option:contains("Newest")').each(function(){
   var $this = $(this);

   $this.text($this.text().replace("Newest","Oldest"));    
});​

http://jsfiddle.net/eSa5p/

EDIT: Answer to the new question:

var $newest = $('select option:contains("Newest")');

$('select option:contains("Oldest")').text('Newest');
$newest.text('Oldest');

http://jsfiddle.net/eSa5p/3/