First, you can refer to many banks which have a sign of “EXCHANGE” on the entrance. Second, there are a lot of authorized shops (in the airports, some streets or malls) that are called “Sarrafi” in Iran (which means Exchange). Note that exchanging money in these shops cost you a bit more but is faster. USD, EUR, GBP, AED are exchangeable almost everywhere but for other major currencies some certain banks are available.
Iran is not connected to the international banking network yet, so you cannot use foreign credit cards. Hopefully, according to the new financial laws, they are solving this problem soon. We recommend you to bring money in cash in form of USD, EUR or GBP.
Iranian Rial is the Iranian currency that is official unit used in documents and cashes. Toman is another money unit in Iran and is equivalent to 10 Rials. Toman is more common in oral and shops.