public Game1()
        {
            graphics = new GraphicsDeviceManager(this);
            Content.RootDirectory = "Content";
            graphics.PreferredBackBufferWidth = 1280;  //délka okna  
            graphics.PreferredBackBufferHeight = 720;  //šířka okna  
            graphics.ApplyChanges();     
            //graphics.ToggleFullScreen();  //celá obrazovka     
            Window.Title = "Snake";   //titulek okna 
        }
        
        ...
        
             protected override void Update(GameTime gameTime)
        {
            // Allows the game to exit    
            if (GamePad.GetState(PlayerIndex.One).Buttons.Back == ButtonState.Pressed)
                this.Exit();

            // TODO: Add your update logic here        
            if (keystate.IsKeyDown(Keys.Space)){
          graphics.PreferredBackBufferWidth = 1024;
            graphics.PreferredBackBufferHeight = 768;
            graphics.ApplyChanges();      //změna rozlišení    
          }