A list of your group's ladders is available after clicking the ladders section from the "Start Organizing" menu and choosing your group. The list contains the ladder's title, status (draft, active, closed, or stopped), a statistics button to view overall ladder statistics (number of activists exited and number currently waiting), a hide button to hide the ladder from your view, and a duplicate button.
Duplicating a ladder will make a copy of all of its steps and put the new copy into draft, so it can be further edited. In this way you can make changes to an existing, published ladder despite the editing restrictions after a ladder is published. You'd copy the active ladder, edit it and make your changes, publish the new ladder, and set the old one to closed so no new activists enter it and new activists only enter the new, active one.