As you have an existing license you are currently grandfathered in under the old agreement. This will let you upgrade your existing instance just by downloading the latest version and running the installer. It will take care of the rest.
I would recommend that you make sure you have a current database backup and a copy of your master key before commencing the upgrade, as without those you may not be able to rollback in case of any problems.
I hope that helps, please let me know if you have any other questions,