Firstly, do you want the subform to be invisible or hidden? If it is invisible it still takes up physical screen space. Hidden will remove it altogether.
Regardless, edit the change event in your checkbox to hide and show the subform
checkbox1 - change - javascript:
if(checkbox1.rawValue == "1") //show subform when checkbox1 is checked
{
subform1.presence = "visible";
}
if(checkbox1.rawValue == "0") //hide subform when checkbox one is unchecked
{
subform1.presence = "invisible"; //or subform1.presence = "hidden";
}