I would do this by setting my return value to be formatted as Y-m-d and then I would format the date/time the way I want by using PHP function date() and strtotime(). The reason for setting the display to Y-m-d is because this is a format that will not be confused when using strtotime()
$acf_date = get_field('my_date_field');
// format date
$date = date('l d F Y', strtotime($acf_date));
// OR
$date = date('F Y', strtotime($acf_date));
http://php.net/manual/en/function.strtotime.php
http://php.net/manual/en/function.date.php
