This is one of the easiest layout changes you can do with Caravel. To resize a row simply move your mouse cursor to either the far left or far right of a row. A vertical orange line should appear and your cursor should change. Simply click and drag to resize the row.
Resizing a column
Resizing a column is quite similar. Just move your mouse to a columns inner border and once again a vertical orange line should appear and your cursor should change. Drag and release to resize the row.
Tip: You can specify an exact width for a row or column in pixels or percent by choosing Row Widths or Column Widths from the Row's Add menu.