Yes, you may upgrade at any time by creating a new support ticket letting us know exactly which plan you would like to upgrade to. It is free to upgrade and the only charge would be the price difference in the plan you upgrade to. For example, if you were paying $5.00 per month with your previous plan at H4Y, and the new plan is $10.00 per month, you'd only pay the $5.00 per month difference for your first month.
If you plan on upgrading to a product that is not within the same product line as your current product, you will have to make a new purchase for the new product, as the pro-ration does not apply when upgrading to a new service.