Spline Replace
The Spline Replace tool will replace any curved element (arc, circle, polyline, spline, Bezier curve, or ellipse) with a spline.
Select the Spline Replace tool on the ribbon or press Shift + S. Any elements that are not allowed for this tool will be dimmed.

Set the tolerance you want to use using either the slider or the edit field. When you mouse over an element, you will see a preview of a Spline fit within your tolerance. Click the element to accept the replacement. You can also marque select multiple elements. Left click, drag the marque, and release. Elements will be previewed as you drag. When you release the new elements will be created.

