asp.net control refresh by c#

asp.net
<asp:ScriptManager ID="ScriptManager1" runat="server">
</asp:ScriptManager>
<asp:UpdatePanel ID="UpdatePanel1" runat="server">
    <ContentTemplate>
        <asp:Button ID="Button1" runat="server" OnClick="Button1_Click" Text="Button" />
    </ContentTemplate>
</asp:UpdatePanel>

c#
Button1.text = "123";