Fourteen days, arranged by phone
Stocked items can be returned within 14 days of purchase for a refund, credit or exchange. Call +44 (0)208 386 6960 and arrange it. Do not send a pack of removal cartons back without that call.
A fault found later
The terms ask for notice of a defect within 14 days of discovering it, and no later than 30 days from delivery. A crushed carton that was obvious on the doorstep is a delivery issue. Call then, too.