It's not necessary to uninstall a previous version of Final Draft, but it's also not necessary for the older version to be installed before you install the newer version. if you leave the older version on your computer, it's just going to take up some hard drive space. Note that on Windows, if one version of Final Draft is open, no other version will open.
If you do want to uninstall the older version, make sure to uninstall BEFORE you install the newer version. If you don't, it's possible for the uninstall process to remove components installed by the newer version and this can leave you with an incomplete installation of the newer program.
IMPORTANT: Before you uninstall an older version, be sure to deactivate it. Simply open the program, go to Help > Deactivate and follow the prompts. Note that your computer must be connected to the internet.
IMPORTANT: If you've started a script and are in production, you should complete the project in the version in which it was created. We don't recommend switching software of any kind in the middle of a job for any reason.