I'm not sure whether you're just trying to view your actions ordered by due date, or to actually change the order of the actions in your project.
If you're just trying to view your actions by due date, you can switch to context mode and group or sort your actions by due date. (If you only want to see the actions for a single project, you can focus on that project before you switch views.)
If you're wanting to change the order of your actions in your project, you can select them and then choose Edit->Sort->By Date Du…—uh, wait, sorry: apparently we didn't include "Date Due" as a sorting option when we added the ability to sort the selection. Sorry, please send us some feedback at firstname.lastname@example.org
if that's something you'd like!