You can easily copy a specific layer or the entire design content from one design to another!
Simply select all of the elements found in the design using CTRL+CLICK or CLICK+DRAG to select the content and copy it to your clipboard ( CTRL+A / CTRL+C).
Then in the same tab create a new design, select your desired size and once the canvas has loaded, hit CTRL+V on your keyboard to paste the layers.
Can I copy layers in the Generator?
This practice is not recommended while working on a design in the Generator because of the way the elements are sourced from the library, creating a high probability for the design to crash due to a corrupted or improperly sourced layer.