This feature is available in Catalyst, Enterprise, and Ultimate editions.
If you need to change a sprint/iteration schedule, you can do so following the instructions below.
Before you Begin
Keep the following in mind:
You must have Project Administration rights on this project
The project cannot have any existing scheduled backlog in any sprint/iteration.
From the Admin menu, select Projects > Iteration Schedules.
Modify the iteration schedule as needed, and then click Save.