Check the following online help article: http://www.telerik.com/help/aspnet-ajax/moss-deploying-radcontrols.html
. It's for MOSS, but it is applicable in SharePoint 2010 and 2013.
Here is one more helpful resource Create an AJAX-enabled SharePoint WebPart that uses RadControls
All the best,
the Telerik team
If you want to get updates on new releases, tips and tricks and sneak peeks at our product labs directly from the developers working on the RadControls for ASP.NET AJAX, subscribe to their blog feed