My Samsung 55 smart TVs shows iTunes movie with black bars top and bottom When playing through older Apple TV, how can I get rid of these bars ??

Many movies have a wider screen shape than your TV and so, in order to show the whole picture, are 'letterboxed' as you describe. Most TVs have an option to zoom the image so that it will fill the height of the screen, though of course you will lose some of the image off the edges. Older films in the classic 4x3 shape are 'pillarboxed' - black panels at the sides - for the same reason. Zooming these will of course cut off the tops of people's heads and so on.

What is your model Apple TV? Identify your Apple TV model - Apple Support

For the Apple TV (4th generation or later), you may double-tap (without clicking) the center of the touch surface of the Siri Remote, to zoom in to match the content height to the height of the screen. It also works for 4:3 content to match the width of the content to the width of the screen.

Personally, I’d like to see all that the director intended, and not zoom in and cut off any parts.