There are several screen layout options available when you're in a meeting. Different layouts are available when content is being shared. You can change your layout by selecting another one from the Layouts menu.
Different layouts may be available depending on your device and the size of the meeting, and whether or not content is being shared. Read this article for a description of how each layout appears, and when it is available to you.
To change your current layout:
Tap the Layout button on your screen, to open the layout menu.
Select the layout you want to use from the menu.