Open the Pages window using the button in the LiveEdit bar.

The left side of the screen has a series of silver bars representing your pages, and at least one light blue box with a blue title at the top.

These blue boxes are your Menu Areas; the name at the top is the name of the Menu Area, and the pages inside the box are pages that exist within that menu.

To move a page between these Menu Areas, click the silver bar representing the page you want to move, and drag it to the desired Menu.