Cut them to the shortest layer, or trim gradually like Kia said, until you get to what was the shortest layer. Th e real challengeis finding ad sticking with a stylist for trimming that understands what you want to do, andthat someone doesn't "trim the layers" so that they reinforce them as it grows out.
Well I have layeres as well that I have been struggling to grow out. And as Tracy mentioned, the key seems to be in trying to find a stylist that understands my objective and follows the game plan. Instead of someone who wants to re-cut the layers back into my hair.