Click on Tools / Deactivate and follow the instructions. Once deactivated, CaseComplete can be installed and activated on your new machine using the same serial number that you originally used. If you don't know your serial number, find that by following these instructions before deactivating. If you no longer have access to the old computer, please submit a support request.
You can also check to see what version your serial number is valid to activate by entering it into the Serial Number Status page.
If you need to install an older version on your new computer, you can download it here. Otherwise download the trial version, which is the same as the latest full product version. Once installed, activate it using Tools / Activate.