You can upgrade your product to Bundle whenever you want simply by paying the cost difference. You only have to send us an email at support@creative-tim.com in which you specify the product that you have, the OrderID, and the Bundle that you want instead. We will give you a unique coupon for the upgrade.
For example: if you paid $49 for Material Dashboard PRO (Freelancer license) and now you need the Big Bundle (Freelancer license), which is $249, you will only pay $200.