I went to the lecture but still cannot level up.
Have you continued an old save game or start a new game? If you have used an old save there could be uncontrolled behavior. There is also a problem with "the new game" option in game, when you have loaded a save before and use the "exit/start new game" ingame option. Then you have not a new game, you have only a new intro sequence and continue on the loaded game states before. If you want to start a real new game, you need to hardreset the game-engine (close and restart then game).