To Modify a Spline's Controlling Polygon
You can modify a spline by using its control polygon (the polygon that the system creates to surround the spline when you first create it). The control polygon displays in white when you choose the Control Poly command.
1. Select the spline, and then right-click to display the shortcut menu.
2. Click Sketch and then click the arrow next to 
Spline.
Spline.3. Click 
Edit Spline. The MOD SPLINE and MOVE PNTS menus appear in the Menu Manager.
Edit Spline. The MOD SPLINE and MOVE PNTS menus appear in the Menu Manager.4. Click > .
The spline’s control polygon appears in white. Spline control points appear with line segments between them on the spline. The line segments begin and end at the startpoint and endpoint of the spline, and intermediate segments remain tangent to the spline. These line segments are visual aids for modifying the shape of the spline.
 | You cannot use this command on a spline that has a tangency condition defined for one end only. |
5. Adjust the shape of the spline by selecting a point on the control polygon and dragging it to a new location. You cannot select endpoints. The spline rubber-bands to its new shape as you move the point.
6. Place the control point by pressing the left mouse button.