Upgrading is a simple procedure from the Client Portal that you can do yourself at anytime. When you place an upgrade or downgrade order, you will be refunded what you haven't used of the current cycle on the existing product/service and then charged for the remainder of the cycle at the new product/service price. The next due date doesn't change.
In order to place an upgrade/downgrade order, you must login to the client area, go to My Products/Services, click the View Details button next to the product or service you wish to manage and then click on the buttons to either upgrade the Package or upgrade the Configurable Options.