Lando wasn't wearing Han's clothes. He was wearing his clothes.
Everyone always asks why was Lando wearing Han's clothes. Han was a barely scraping by, stuck-up, half-witted, scruffy-looking nerf herder. That guy could barely keep his ship together. You really think he is going to be spending money on nice clothes? Nope. But we do know someone who has style, and had the money to spend on it. Lando.
Where would Lando keep a lot of his clothes? Probably on his ship. And what ship was that? The Millennium Falcon. And who ended up with the Falcon? Solo. And after Solo was captured, who got the Falcon back? Lando. And what came back into his possession? The clothes that were on the ship.
It also makes sense that Luke was wearing Lando's clothes at the end of Ep IV. You think a farm boy has that jacket? Luke didn't bring a change of clothes anyways. No other rebels had that jacket, so it probably came off the Falcon. I can imagine Han and Luke getting ready for the ceremony and Han wanting to brag and puffing up his newfound hero status. "Hey kid, you can't go to the ceremony looking like that. You know what, I'll help you out here. Go check out the Falcon for some clothes. You know, I won the Falcon from this guy in a card game. I got all his clothes with it. These clothes I'm wearing, they came from his closet. Let me tell you, I really took him for all he had. Haha. You should have seen his face when I pulled off that win. Stick with me kid, I'll teach you all you need to know about your big galaxy."