There are cases when you may want to update the information inside the grid by triggering a callback externally from other control on the page. Generally, this is a simple task with the integrated AJAX mechanism of Telerik RadGrid. You need to make a call to the RadGridClientObject.AjaxRequest() method (passing the necessary information as parameters to it) and then override the RaisePostBackEvent method to apply the changes.

To understand the specifics when raising postback event from webform/user control you can follow the link below:
Raising asynchronous postback request