Click the Features | Change | Change To | Polygon to Polyline command or right-click on a polygon and click Polygon to Polyline to convert one or more selected polygons into polylines. Each selected polygon is converted to a new separate polyline.
The new polyline retains the line properties from the polygon. If the object name has not been changed from the default Polygon, the object is renamed Polyline. If the object name had been altered, the custom object name is retained.