apple class:
 public void levelSpeed()
    {
        
        if(Score.Score==50)
        {
             setLocation(getX(),getY()+7);
        }
    }
counter class:
public class Counter extends Actor
{
    int score = 0;
    /**
     * Act - do whatever the Counter wants to do. This method is called whenever
     * the 'Act' or 'Run' button gets pressed in the environment.
     */
    public void act() 
    {
        setImage(new GreenfootImage("Score : " + score, 24, Color.GREEN, Color.BLACK));
        level();
    }
    
    public void addScore()
    {
        score++;
    }
    
    public void level()
    {
        if(score==50)
        {
            setImage(new GreenfootImage("LEVEL 2", 60, Color.WHITE, Color.BLACK));
        }
    }