Composite's available documentation is pretty thorough and helpful. I would highly recommend that you read through it all as it will give you a much better idea of how to best use the Composite CMS. It's a fantastic piece of software with amazing capabilities at customisation and extension, but without knowledge on these topics you may fall short on attempting implementations.
The specific piece of functionality you are targeting is called 'Functions' within Composite. The Carousel you are talking about is most likely implemented using a 'Function'. To change the target folder for the 'Function' you would have to open up the Composite Admin interface, edit your page, and then double click on the 'Carousel Function'. This should display a 'popup' function box editor, with which you can change the target folder selection.
Again this is the basic functionality of Composite described in their documentation. You can view the documentation for functions here: http://docs.composite.net/Functions
I would highly recommend that you read through all their basic user level documentation.