imagebutton postbackurl parent window

I have this imagebutton that is wrapped around jquery modal in an iframe with some checkboxes. The user selects the appropriate checkboxes and clicks register. I want to open the registration form in the parent window...
<asp:ImageButton runat="server" ID="btnregister" ImageUrl="/assets/images/register.gif" OnClick="btnregister_Click" />

on page_load:


btnregister.PostBackUrl = "~/form/register/new.aspx";

so how do I make the registration form load on the parent window? any idea?

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