1) get a reference to the RadWIndow from inside. This is done with the famous GetRadWindow function that can be seen here
2) use the client-side API
of the control - the set_title(string) method
If you obtain the new title on the server you can store it in a hidden field, for example. The ready function can be called from the server by following this help article
or by using the ResponseScripts collection of the RadAjaxManager if you are using one.
the Telerik team
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