Thank you for your interest in Telerik's Silverlight Controls . Changing themes is easy - you just have to add the needed theme to the references and then use the following :
is a reference to Telerik.Windows.Controls .
How to set theme from the code-behind or set it for the whole application you can learn from our help here
. It is all explained in this topic.
Hope that helps. If you need more help please let me know.
the Telerik team