Moving a design is done by clicking and holding the top-right corner of the design in the design folder. While still holding your click, you will be able to drag and drop your project to any other sub-folder. After the page has been moved to a new sub-folder, you will receive a notification of the move in the bottom right corner of your screen to confirm that the project has been moved.
To learn more about duplicating a design, check out our article on Duplicating a Design.