<style>
.loginFormInitialStyle{
   height:140px;
   width:150px;
   background-color:blue;
}
.loginFormChangeStyle{
   height:500px;
   width:150px;
   background-color:blue;
}
</style>

<div ng-class="loginForm"></div>

$scope.loginForm = {"loginFormInitialStyle":true, loginFormChangeStyle:false}

$scope.onClick = function(){
   $scope.loginForm = {"loginFormInitialStyle":false, loginFormChangeStyle:true}
}