Change label text which is inside updateprogress from code behind

Hi ,

How to change label text which is inside updateprogress from code behind ? 

I tried with this code , but it did not work ? 

Label ProgressMessage = UpdateProgress1.FindControl("lblProgressMessage") as Label;
if (ProgressMessage != null)
{
ProgressMessage.Text = "10% ";
}

Value of lblProgressMessage changes in code behind. but its not displaying in web page

Please help me out