Any shape can be resized, rotated or moved once it’s been placed upon the Drawing Stage. You can use the little squares that appear in any selected shape’s boundary box’s corners or midpoints to extend the dimensions of the shape. Just click and drag them. To rotate a shape, click and drag the curled arrow that you’ll see above the selected shape.
Also worth noting is the ability to lock a shape to its current dimensions. To do this mark the “Lock Shape” box in the shape’s Properties Panel that appears to the right of the shape. (Using Gliffy Online, you can also right click on a shape and select “Lock Shape” from the context menu).
When you lock a shape, the little squares around the boundary box turn red to indicate the shape is fixed. You will not be able to change the dimensions, or other properties, of the shape until you unlock the shape.