The RadUploadItem inherits the ListBoxItem class thus allowing a selection of RadUploadItems.
By default the RadUpload doesn’t display the selected RadUploadItems. To enable the user to see the selection you have to set the SelectionVisibility property to Visible (its default value is Collapsed).
[XAML] Example 1: Setting the selection visibility
<telerik:RadUpload x:Name="radUpload" SelectionVisibility="Visible"/>
The RadUpload control also lets users select single or multiple RadUploadItems by simply setting the SelectionMode property. The SelectionMode property is a SelectionMode enumeration which exposes the following members:
Single - use it for a single selection. At this mode the user will be available to select only one item at once.
Multiple and Extended - use these values when you want the user to be able to select multiple items at one time by holding down the control key and clicking multiple items with the mouse or by using the keyboard. A second click on a selected item will unselect that item.