Click the Specialize Link button 
on the diagram toolbar.
Click the source element.
Drag the link to the destination element.
Drop when the destination element is highlighted.
You can draw a specialize link between any use case elements.
To create a specialize link:
Click the Specialize Link button
on the diagram toolbar.
Click the source element.
Drag the link to the destination element.
Drop when the destination element is highlighted.
Related Topics:
Creating Links
Moving Links
Editing Links