To deactivate Final Draft 8:
Open the program and go to Help > Deactivate. If you have an internet connection, choose Online Deactivation. The program will connect to our system and the activation will be taken off the computer and placed back into your account on our server. You can use this same activation for another computer or for this one if you're planning to, for example, reformat the hard drive or upgrade your operating system.
See this article if the activated computer doesn't have an internet connection: How do I manually deactivate Final Draft 8?