QGIS 3.10 Page settings won't except changes of page size A3

The right click option works when you first create a new layout, but it doesn't seem to work if you're trying to edit an existing layout. Right-clicking on an existing layout only gives grayed-out menu choices of undo and redo. When you open up a new layout, before adding any information to the layout, you can right-click and see the Page Properties option, along with a functional "Manage Guides for Page" option. It also provides the grayed-out menu choices of undo and redo, as well as a grayed-out "Remove Page" option.