If you need to re-install Lectora or move Lectora to another computer you must first uninstall it from the current computer. Use Add/Remove Programs within the Windows Control Panel, while connected to the Internet. This will ensure that the software releases the license for future installation.
Please be sure to copy the license key by writing it down or taking a photo of it. When you install Lectora on your next system, ensure you are connected to the internet during installation, then enter that same license key and it will be validated during the install process.
When a system in my department crashed, we were able to recycle that Lectora license by calling Trivantis support. They can manually mark it as available. (Obviously, I have no idea how they do it from their end.)