You can change the layout (grid, irregular...) of images in almost any Posterino document. The initial layout of images right after creating a new document from a template is just a handy start configuration.
Basic layout methods like grid, irregular and random look like this:
To change the layout of images in your document:
From thepanel choose a layout option (Grid, Irregular...) by clicking on a layout icon or name:
The placement of images will be adjusted to the new layout automatically.
Alternatively you can choose a layout method using the menu: Go to> > (Command-1 .. Command-6).