If you have checked bags you need to collect your bags in terminal F and take the inter terminal shuttle to get to Marta. It sucks.
What sucks additionally (at least as of last time I flew in via AC which was a couple of months ago) is that they no longer have a shuttle from International to the Car Rental Center. So now if you leave the secure area at F, you need to take a shuttle all the way to the main terminal, then take the train from there. It stinks.