You can't change iron into gold.

你不能把铁变成金。

I want to change dollars into pounds.

我想把美元换成英镑。

A:Yesterday I bought a sweater from your store.and I'm afraid it's too small. So I want to change that into a bigger one.

昨天我在你们店里买了一件毛衣，我恐怕它太小了，我想换个大一点的。

B:Ok,wait a minute.

好的，请稍等。