<telerik:RadScriptBlock ID="RadScriptBlock1" runat="server">
    <script>
        function pageLoadHandler() {
            // Get reference to RadGrid
            var grid = $find('<%=RadGrid1.ClientID %>');

            // Find the Pager Wrapper element
            var $pagerWrapper = $(grid.get_element()).find('.rgPager .rgWrap.rgAdvPart');

            // Find the GoToPage Button within the Grid element 
            var $goToPageButton = $($pagerWrapper).find('.rgPagerButton[id$=GoToPageLinkButton]');
            var $changePageSizeButton = $($pagerWrapper).find('.rgPagerButton[id$=ChangePageSizeLinkButton]');

            // Attach the click event listener to the button
            $goToPageButton.on('click', function (e) {
                // cancel the click event
                e.preventDefault();

                // Get the Current Page 
                var currentPage = grid._currentPageIndex + 1;

                // Find the GoToPage Numeric TextBox
                var goToPageTextBox = $telerik.findControl($pagerWrapper[0], 'GoToPageTextBox');

                // Condition to check if the TextBox has a value and the value is different from the CurrentPage
                if (goToPageTextBox.get_value() && goToPageTextBox.get_value() != currentPage) {
                    // fire a Custom command using the fireCommand() method
                    // pass two arguments to the method: CommandName, CommandArgument (e.g. the Page number)
                    grid.get_masterTableView().fireCommand("GoToPage", goToPageTextBox.get_value());
                }
            })

            $changePageSizeButton.on('click', function (e) {
                // cancel the click event
                e.preventDefault();

                // Find the ChangePageSize Numeric TextBox
                var changePageSizeTextBox = $telerik.findControl($pagerWrapper[0], 'ChangePageSizeTextBox');

                // Get the Current PageSize
                var currentPageSize = grid.get_masterTableView().get_pageSize();

                // Compare the Current Page Size with the TextBox value, if not identical
                if (changePageSizeTextBox.get_value() != currentPageSize) {
                    // fire a Custom command using the fireCommand() method
                    // pass two arguments to the method: CommandName, CommandArgument (e.g. the New Page Size)
                    grid.get_masterTableView().fireCommand("ChangePageSize", changePageSizeTextBox.get_value());
                }
            })

            // Sys.Application.remove_load(pageLoadHandler);  
        }
        Sys.Application.add_load(pageLoadHandler);
    </script>
</telerik:RadScriptBlock>

protected void RadGrid1_ItemCommand(object sender, GridCommandEventArgs e)
{
    var grid = (RadGrid)sender;
    // If the CommandName is the one we triggered manually
    if (e.CommandName == "GoToPage")
    {
        // get the Page number from the arguments
        var pageNumber = int.Parse(e.CommandArgument.ToString());

        // Change the Grid's Page Index based on the Page number
        // Extract one from the Page number as the Page indexes start from 0.
        // Index of 0 being Page 1, Index 1 being Page 2, etc...
        grid.CurrentPageIndex = pageNumber - 1;
    }
    else if (e.CommandName == "ChangePageSize")
    {
        // get the Page number from the arguments
        int pageSize = int.Parse(e.CommandArgument.ToString());
        // Change the Page Size using the new value
        grid.PageSize = pageSize;
    }
}

Protected Sub RadGrid1_ItemCommand(ByVal sender As Object, ByVal e As GridCommandEventArgs)
    Dim grid = CType(sender, RadGrid)
    'If the CommandName is the one we triggered manually
    If e.CommandName = "GoToPage" Then
        'get the Page number from the arguments
        Dim pageNumber = Integer.Parse(e.CommandArgument.ToString())
        'Change the Grid's Page Index based on the Page number
        'Extract one from the Page number as the Page indexes start from 0.
        'Index of 0 being Page 1, Index 1 being Page 2, etc...
        grid.CurrentPageIndex = pageNumber - 1
    ElseIf e.CommandName = "ChangePageSize" Then
        'get the Page number from the arguments
        Dim pageSize As Integer = Integer.Parse(e.CommandArgument.ToString())
        'Change the Page Size using the new value
        grid.PageSize = pageSize
    End If
End Sub