I writed this example using jQuery:
$(document).ready(function(){
// You can change for your classes or add this in your smarty template
var month = $('.month'),
day = $('.day'),
year = $('.year'),
out = $('.out');
var months = {
'JAN': '01'
'FEB', '02',
'MAR': '03'
// etc...
};
// Hides the unecessary elements
month.hide();
year.hide();
day.hide();
out.html(months[month.text()] + '/' + day.text() + '/' + year.text());
});