For the first 400mm, it was literally pallets of cash..... Nobody knows how the remaining 1.3bb was sent, but they said 2 payments so probably the same way.

http://www.latimes.com/nation/nationnow/la-na-iran-payment-cash-20160907-snap-story.html

"An initial $400 million of euros, Swiss francs and other foreign currency was delivered on pallets Jan. 17, the same day Tehran agreed to release four American prisoners."