In order to upgrade from Trial to Purchase version of the Telerik Silverlight controls just uninstall the Trial version and after that use your Telerik account in order to download the purchased installer (.msi file).
Install the product and after that use our Upgrade Wizard in order to upgrade the project you are using now.
As for the replacement of the dll files you could find more information here: http://www.telerik.com/help/silverlight/installation-upgrading-from-trial-to-developer-license.html.
the Telerik team
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