This feature is available in Catalyst, Enterprise, and Ultimate editions.
By default, Storyboard story cards display in rank order within each status column. Using drag-and-drop, you can change the priority by dragging and dropping it up or down within a column. Note that story ranking changes carry through to all other views in the system.
Select Team > Iteration Tracking (or Sprint Tracking) > Storyboard.
Drag and drop each story to the desired location on the Storyboard.