Change check value checkbox form ( Awesomium VB.net)

I tried both, but it won't work. Can anyone help me?

WebControl1.ExecuteJavascript("document.getElementById('#signupForm_confirm_terms').prop('checked'", "true")

WebControl1.ExecuteJavascript("document.getElementById('#signupForm_confirm_terms').attr('checked'", "true")

Thanks in advance :)