Absolutely!

For example, if you start with our Cheap plan, but decide you want to host more than one website, or that you require more disk space, a few months later, you can choose to upgrade at that time. Our billing software will automatically calculate how much of the Ultimate plan you've paid for and put it towards the price of the new Personal plan.

Keep in mind that the upgrade to your billing account occurs immediately, but your hosting limits are manually updated by our support staff for both web hosting and shoutcast hosting accounts. This means it is best to ensure you complete your upgrade at least 24 hours before you are projected to reach your limit. The sooner the better!