1To succeed, relieve, or replace someone (to take over someone's role or duty).
看護師が夜勤で同僚に替わった。
A nurse relieved her colleague on the night shift.
先輩は明日から新しい部署に行くので、私が替わることになった。
My senior is moving to a new department tomorrow, so I'll be taking his place.
2To take the place of or substitute for someone; to represent or take over (including handing the phone to someone).
田中さんに替わって説明します。
I'll explain on Mr. Tanaka's behalf.
すみません、少し席を外します。誰かに替わってもらえますか？
Excuse me, I'll be away for a moment. Could someone cover for me?
電話が鳴ったので母に替わってもらった。
The phone rang, so I had my mother pick up.
3To be exchanged or to change places with someone; to switch or swap positions.
席を替わってくださいませんか？
Could you please change seats with me?
彼らは役割を替わって演技した。
They swapped roles and performed.