Select the Template you wish to edit (for example, the Archive template).
Expand the WP Loop box and look for the Post Box within it (the full name of this box may vary according to your Skin); hover over this box until the down arrow appears to its right, then click that to expand the box.
Click show tray ↓ to view the list of dependent Boxes for the Post Box.
Click Post Box → Content to add it to the active area of the Post Box; then drag it into your preferred location within that Box.
If necessary, use shift+drag to remove Post Box → Excerpt from the template (by dropping it into the gray box on the top right side of the screen).