RadDiagram gives you the ability to remove RadDiagramItems interactively, programmatically or with DiagramCommands.
Please note that the examples in this tutorial are showcasing Telerik Windows8 theme. In the Setting a Theme article you can find more information on how to set an application-wide theme.
You can remove the selected RadDiagramItems by pressing the Delete Key.
Below you can see the result of delete operation over the selected RadDiagramItems:
You can remove RadDiagramItems in code behind by using the RadDiagram.Items collection and its Remove() or RemoveAt() methods:
You can use the DiagramCommand "Delete" in order to remove the selected RadDiagramItems.
For more information on this, please check out the Commands article.