How can I change a HTML tag from Combobox
===

I have an aspx page. which is shortly:
   
    <html>
    <head>
    </head>
    <body>
    <h1> Stack Overflow </h1>
    </body>
    </html>

and there is RadCombobox;

     RadCombobox1.Items.Add(new RadComboBoxItem(){ Text = "Stack", Value = "1" });
     RadCombobox1.Items.Add(new RadComboBoxItem(){ Text = "Overflow", Value = "2" });
     RadCombobox1.Items.Add(new RadComboBoxItem(){ Text = "Stack Overflow", Value = "2" });

When I select second Item which is "Overflow" in my example, 
how can I change < h1> tag?
I want to show in < h1> tag , what I choose from combobox..