UPDATE: Apparently exchanging from rare to ultra rare will ONLY give you one of the three skins listed below, and not any ultra rare skins from crates.
Another major addition with this update is the Item Exchange, from here you can trade in your account skins for a rarer one, the ratios as described in the latest livestream were five common (green) for a uncommon (blue), four uncommon for a rare (purple), and five rare for a ultra rare.
The items you get out are also dependant on the items you put in, if you put in two items from the Invitational Crate and two items from the Alpha Launch crate, then its a 50% chance of getting an item from either of those crates. If all items are from the same crate, you will receive an item from that crate only.
Exchanging from rare to ultra rare will award one of these three unique skins: