When starting a new project from a template (as opposed to the single Chart/Map buttons in your Library), you basically choose your project canvas size - infographics and reports are vertical, dashboards - horizontal, and you are, of course, able to enter custom project page size under each of the templates. This is an important part of the new Infogram layout where you can freely position objects around your page, so setting the page dimensions right from the start will save you from any unnecessary chart reordering if changing project layout amidst an already started project.
However, if you have started your project already and want to change the project canvas size, this can be easily done in two ways:
1. Deselect any charts and images and click on the Settings tab in the right sidebar where under the theme selector there will be a drop-down to switch to other canvas size or enter a custom size.
2. Hover the edge of your project canvas with your mouse - an arrow will appear showing that you can drag this edge to resize your project.
If, however, you have started your project by clicking the single Chart/Map button in your Library or are editing an older infographic created before the new templates became available, you can adjust your project's width by deselecting any charts/objects in your report and adjusting the slider in the right sidebar. In this layout the height/length of your project depends on how many charts and other objects you add into your project, however you can adjust chart height by selecting them and adjusting the slider in the right sidebar.