The whole magic of Posterino unfolds in the layout (or blueprint) mode. Here you can change most aspects of your document.
To go into Layout mode:
You are in Layout Mode when you see the blueprint view:
In Layout Mode you can customize the general look of your document. You can for example change the image frame or the layout method used for placing your photos. To do so, click on any of the highlighted areas in the blueprint and a popup will open showing customization options. For example the
popup: