1Changing into different clothes, or the spare clothes prepared for that purpose. Can also appear as 着替えをする / 着替えする to describe the act of changing clothes.
旅行用のかばんに着替えを二日分入れた。
I packed two days' worth of spare clothes in my travel bag.
保育園には毎日着替えを持たせてください。
Please send a change of clothes with your child to daycare every day.
プールに入る前に、更衣室で着替えをした。
Before getting in the pool, I changed clothes in the locker room.
汗をかいたので、家に帰ってすぐに着替えした。
I'd been sweating, so I changed clothes as soon as I got home.