How to change pages through event in Button inside UpdatePanel?

I have a page inside an "iframe" on this page there is a form with a button. The button is inside an "UpdatePanel" to show me in case there are some empty fields "labels" of "required field" that are also inside the "UpdatePanel". If the fields of the form are full when you press the button when generating your event, you should change it to another page.

Within the event of the button I have implemented the following code to change the page that works for me only if the button is outside the UpdatePanel.

Type cstype = this.GetType();
String csName = "RedirectScript";
String script = "window.parent.location = '../Paso2.html'";
ClientScriptManager cs = Page.ClientScript;
cs.RegisterClientScriptBlock(cstype, csName, script.ToString(), true);

I tried to change pages with Response.Redirect ("../ Paso2.html"); but in this case it does not work with the button inside or outside the "UpdatePanel"