After you purchase and install FL STUDIO, the easiest way to unlock it from Trial Mode, is to enter your Image-Line Account login details on the FL STUDIO Help (menu) > About panel and restart FL STUDIO. That's it! Do this after every update, or fresh install, and you will be ready to enjoy your Lifetime Free Updates:
Unlocking FL Studio on a non-internet connected computer? See here.
About Updating FL Studio
To update FL Studio, download the latest installer and run it. If you are installing the same major release number (FL Studio 20 to 20.1 for example), this will install over the existing installation and update it.
If you are installing a major update (FL Studio 12 to 20 for example), this will install in parallel. In this case we have an in-depth tutorial on how to manage the transition of all your project related data here.
Good news! From FL Studio 20, we changed where your user data is saved. On both Windows and Mac computers it now resides (by default) outside the FL Studio installation in ...\Users\[your computer account]\Documents\Image-Line\FL Studio. This location is set by your User data folder option and means updating FL Studio 20 is much simpler, as you don't need to migrate custom user data, plugin databases and related information. See here for details.