To Substitute, To Switch, To Exchange
transitive verb, ichidan verb
Because the hiragana ends with an う sound, you know this word is a verb. The kanji itself means replace so the verb vocab version is to replace. You know that you're doing the replacing because of the air (える). You're replacing the air as quickly as you can because if you don't you wouldn't be able to breathe in this small room.
替える means to replace something with another item of the same kind or equivalent, rather than changing its state. Wondering how it differs from 代える? While 代える stresses that you’re using someone or something “in place of another,” 替える simply indicates the act of swapping one thing for another similar thing.
The reading is the same as the one you learned with the kanji.
I already asked dad to replace the light bulb.