Exchanges and returns

Can I exchange an item? Can I return my order? Can I try the items on at home and still return them? How do I return or exchange my order? Where is my return? When will I be refunded? What happens to my Klarna or PayPal invoice when I return? Do I have to pay for my return? Can I return an item I bought on sale? What if my item is defective, damaged or the wrong one?