After a 2-month test period, we have given all the Zemanta One (Z1) users access to our new Creatives management system called Creative Library! 

It enables you to upload creatives just once and then use them across all of your campaigns and ad groups.

The new Creatives management is completely replacing the old system with better workflows when adding, editing, exporting, and using your creatives. You can find the instructions on how to use Creative Library here.