delete model

router.js

movieDb.Router  = Backbone.Router.extend({
        routes:{
            '':         'landPage',
            'home':     'landPage',
            'login':    'login',
            'signup':   'signup'
        },

        landPage: function(p){
            $('div#homepage').empty();
        },

        login:  function(p){
            this.cleanup()
            this.current = new loginViews();
        },

        signup: function(p){
            this.cleanup();
            this.current = new signupViews();
        },

       cleanup: function(p){
           // Tells the current view it's not needed anymore.
           // This way, you can do some cleanup steps by overriding the
           // view's `remove` method.
           if (this.current) this.current.remove();
       }
    });