Replace my macbook air adaptor

Sounds like the MacBook Air came with this adapter

30W USB‑C Power Adapter - Apple

and you would like this one

70W USB-C Power Adapter - Apple

For a MacBook Air introduced in 2022 or later, using the 70W adapter would allow fast charging.

Fast charge your MacBook Air or MacBook Pro - Apple Support

I don't think there is a way of exchanging the power adapters after sale (short of returning the laptop and ordering another one with a different power adapter selection) – though I could be mistaken. You could contact Apple and ask them if they would do an exchange (for the extra $20 you would have paid if you had selected the 70W power adapter at ordering time).

You could just buy a 70W one, though.

Karan2004 wrote:

I recently bought macbook air with 30w charger but I want to exchange my 30 w adaptor with 70 w adaptor

You don't say what Macbook Air you have so here is a summary of charging options:

Charge your MacBook Air or MacBook Pro - Apple Support