Jquery class selector is not working-Collection of common programming errors

If you just want to change the ALFL Text , you can do something like this :

var $span= $('span.ui-btn-text');
$span.each(function(){
    if ($(this).text() =='ALFL') {
        $(this).text('A');
    }        
});

Js fiddle Demo : http://jsfiddle.net/95CyN/

If you want to change text/html of all span with class ui-btn-text, do this:

 // change the text inside the element
 $('span.ui-btn-text').text('A');

OR

 // change the html content inside the element
 $('span.ui-btn-text').html('A');

OR

  // Replace the html element
  $('span.ui-btn-text').replaceWith('A');