Automatically set full size for all my images in all my post and page?

You can use the_content filter to filter all post content and replace img sources.

add_filter( 'the_content', 'show_full_sized_images' );
/**
 * Replaces all -600x999 images with full image url
 * @param string $content
 * @return string
 */
function show_full_sized_images( $content ) {

    $pattern = '~(http[^\'"]*)(-600x[0-9]{2,4})(\.jpe?g|png|gif)~i';

    $m = preg_match_all( $pattern, $content, $matches );

    echo '<pre>' . esc_html( print_r( $matches, 1 ) ) . '</pre>';

    return preg_replace( $pattern, '$1$3', $content );
}

You’ll also need to add following css because width may be limited by width attribute in img tag:

img {
    width: auto;
    height: auto;
}