Let's start by explaining that the current Flight Logger is version 3, so when Andrei talks about FL3 he means the current Flight Logger

As for deinstalling Flight Logger, just delete it's folder from your Program Files directory. Yes, it will leave a bit of "mess" in your registry, but that will be corrected when you install it again "over the top".
As for unlocking a PP flight, that's easy. Log into the main EuroHarmony website with your pilot ID and password. Then, from the Divisions menu, go to the ProPilot "division". Once you're in ProPilot, click on "Pilot Information", and at the bottom of the pilot information page you'll see you locked flight (EHM-H1116). Finally, click on the big "Unlock Flight" button there to unlock the flight.
Now, the above en Francais (thanks to Google, so blame them if it's has no meaning):
Comme pour le déverrouillage d'un vol PP, qui est facile. Connectez-vous au site Web de EuroHarmony principal avec votre ID et mot de passe pilotes. Puis, à partir du menu divisions, aller à la ProPilot "division". Une fois que vous êtes dans ProPilot, cliquez sur "Pilot Information", et au bas de la page d'information pilotes, vous verrez que vous verrouillé vol (EHM-H1116). Enfin, cliquez sur le gros "Unlock Flight" bouton là pour débloquer le vol.