French phrase
Je voudrais échanger ~ contre ~.
Meaning
I would like to exchange ___ for ___.
When to use it
A polite request to trade one thing for another. It is common in shops and also applies to bartering or currency exchange.
Example dialogue
Je voudrais échanger ma robe contre une taille plus grande.
I would like to exchange my dress for a larger size.
Bien sûr, vous avez le reçu ?
Of course, do you have the receipt?