This tab is accessed from Theme Administration in Theme Builder 3.0 and above.
To select an alternative default layout, select a layout from the list of layouts in the left-hand side of the interface.
Press the preview button to get a preview of the selected layout.
To assign the layout that you have selected and previewed as the global default layout, press the "use selected layout button".
Ticking the lock layout button does just as it suggests. Locks the layout in place.
Locking the layout will not prevent the possibility of deleting it via the Manage Layouts interface.
Use this to select a layout, preview it and assign it as the default layout for personal spaces in your Confluence wiki.