Open the hitman2.ini file in the game directory and change the parameter:
DefaultScene = AllLevels / logos.gms
DefaultScene = AllLevels / levelmenu.gms
And you will get access to all levels.
In the 1st mission itself, I did this: first I strangled the guard, who from time to time poured. Then he used chloroform to put the postman and the supplier to sleep. When I entered the grounds of the villa, I headed to the right. There will be a guard near the garage. He will go to you, and when he is close, kill him with a pistol with a silencer. Go through the door, wait for the fat man to cast, and bang him off the barrel with a silencer. Take the keys and climb onto the roof. Walk down the roof to Don’s office, but don’t enter yet. Use the card and wait until Don leaves the office. When he’s gone, go to the other side and hide. When Don returns to the office and stops moving (look on the map), open the door and tiptoe up to the mafia. Strangle him. Take the keys and go straight through the door. Go straight through the roof almost to the very edge. Turn right and head downstairs. You will find yourself right next to the stairs leading to the basement. Enter the basement and open the closed door. Look into the camera for Diana to start making excuses. Exit the basement and go to the garage. Hide by car.