Navigation of Forms

Question

Dear Friends ,
                          My application has 2 forms ,namely form 1 & form 2 now in form one if for logging in the application once the log in validations are satisfied then the user needs to be navigated to form 2 .
I have Navigated the form 2 by creating an instance of it
form2 frmSecond = new form2 ();
frmsecond.show();
now the problem what i have is that when the second form is popped up the first form is still active where as i need to have only the second one .
So any helps as of how can i get only one form   to be prersent .