You will need the latest Clooz serial number issued to you (original purchase or renewed update support), along with the unlock password. These would be in the email you received after purchasing the program or renewing update support.
Download the clooz4setup.exe program at http://downloads.clooz.com to your desktop or downloads folder, then execute the setup program.
If your Clooz database (.clz extension in version 4; .cdb in version 3) and any associated media files have not already been moved to the new system, do so now.
Once you enter the serial number and your user name (your preferred identification) into Clooz, you can use the File menu->Maintenance->Media Location Tool to help you reestablish all the proper file links between the Clooz database references and the actual file locations. It’s always simplest if you follow a general practice of keeping Clooz documents within the same folder structure, where the entire structure can be copied to another system and maintain the same file path.