When you need to exchange the resources while participating in a Special Event, you can use the Converter.
To do that, find it on the Main Island of the Event.
Click on it, in the pop-up window in the upper part you'll see the number of resources that you will get after an exchange. Select an option that you want to receive.
Each chest requires a certain amount of resources for an exchange. For example, 1 chest requires 11 items. To proceed with the exchange click on the "add" button (green plus icon) in the upper corner of the item's icon.
Select the amount that you want to exchange and then click on the"OK" button.
You're almost there! When you add the required number of the resources, click on the "Exchange" button.
The exchange itself takes mere seconds. After it's done, you'll see the corresponding chest near the Converter.
Please note: The converter takes the fee, though, so you need 11 Runes to get 8 random ones, for 21 Runes you'll receive 16 new ones and finally, you will require 30 Runes t to get 24 random ones.