If you have a license of formZ 6.7, you can download the installers for formZ 6.7.3 for your operating system from the links below:
If you have not had form·Z installed on this computer / operating system previously, you will need to install the WIBU Runtime Kit, which you can download from half way down this page: http://www.wibu.com/en/downloads-user-software.html.
(If you are using Windows, plug the key in after the WIBU Driver has been installed. If you have virus detection software, don't forget to disable this before installing, and if you are using Windows, you should check to make sure that you have a recent video driver.)
During the installation process, it will prompt you for your existing formZ 6.7 install code to install this.