how to UPDATE REQUIRED PORTION without Page Load Using Ajax Control

Default.aspx

        <asp:ScriptManager ID="ScriptManager1" runat="server">
        </asp:ScriptManager>

        <asp:UpdatePanel ID="UpdatePanel1" runat="server">
              <ContentTemplate>
                       <asp:TextBox ID="TextBox4" runat="server"></asp:TextBox>
                       <asp:Button ID="Button1" runat="server" Text="Button"
                        onclick="Button1_Click" />           
              </ContentTemplate>
        </asp:UpdatePanel>