Change the shape of the Skeleton by moving Joints.
Click and drag the 3D cursor near to the node at the end of the Joint to be stretched. Hold down the left mouse button and click the right button to pick up the node. Drag the mouse (keeping the left button pressed) the node will follow the 3D cursor and the joint will stretch. If the CTRL modifier key is held down while dragging the mouse, all child joints will undergo a rigid body motion.