If you picked up the item from store yourself you must return it with your reciept, however if you had the item through home delivery then IKEA are obliged to collect, the onus is on the customer to prove an item is faulty. You can return an item within 90 days if you change your mind although if the item is not in the original packaging then it will incur a 30% charge as this cannot be resold.
Rgds