You could use:
echo date('F Y', strtotime('20130814'));
which should do the trick.
Edit: You have a date which is in a string format. To be able to format it nicelt, you first need to change it into a date itself - which is where strtotime comes in. It is a fantastic feature that converts almost any plausible expression of a date into a date itself. Then we can actually use the date() function to format the output into what you want.