In addition to Elliot’s suggested method, if you didn’t want to change the value saved to the database, you could use the DateTime ‘format’ method:
$date = get_field("my_date_field");
// assuming your return format is "Ymd"
$dateTime = DateTime::createFromFormat("Ymd", $date);
if ( is_object($dateTime) ) {
$month = $dateTime->format('F');
$year = $dateTime->format('Y');
//...
}