According to the information presented on the Buy page when you hover the What will I receive? menu, you are entitled to a 1 year of free updates. You can continue using the software after the 1 year of updates, but I don't think you will have the possibility to upgrade to a higher version for free which means that yes, you will have to buy the software again.
In some cases, the upgrade is cheaper because you already have a previous version, but it's best to simply ask the developers: https://www.camdevelopment.com/contact.htm
