Instead of; in place of — indicating that one person or thing replaces another.
部長にかわって課長が会議を進めた。
In place of the director, the section chief led the meeting.
新モデルが旧モデルにかわって店頭に並んだ。
The new model replaced the old one on store shelves.
今日は田中さんにかわって私が出席します。
Today I will attend in Tanaka's place.
On behalf of — indicating acting as a representative or agent for someone.
彼にかわってお礼を申し上げます。
Let me offer thanks on his behalf.
社長にかわって挨拶をさせていただきます。
Allow me to give a greeting on behalf of the president.
病気の友人にかわって、彼の荷物を受け取った。
I received his luggage on behalf of my sick friend.