Update Panel On Master Page

I have an Image control a Master Page that the user can change from a content page.  I would like to update  the picture using an update panel, but I dont see how I can trigger it from the content page.

The master page image

<asp:UpdatePanel ID="UpdatePanelParent" runat="server" ChildrenAsTriggers="false" UpdateMode="Conditional"> <ContentTemplate><asp:Image ID="iprofile" runat="server" BorderStyle="Solid" BorderColor="Gold" BorderWidth="1px" style="margin:20px;" /></ContentTemplate></asp:UpdatePanel> 

protected void btnclosepic_Click(object sender, EventArgs e)
    {
        UpdatePanel panel = (UpdatePanel)Master.FindControl("UpdatePanelParent");
        panel.Update();

    }

This is my  attempt at triggering the update Panel - it doesnt work...