I start to change twentyeleven theme and there install Header Image Slider.
To change image size I change header size in theme.
In wordpress\wp-content\themes\twentyeleven\functions.php
// The height and width of our custom header.
‘width’ => apply_filters( ‘twentyeleven_header_image_width’, 1000 ),
‘height’ => apply_filters( ‘twentyeleven_header_image_height’, 288 ),
Height size can be changed when uploading pics in to header/slider.
I hope this will help 🙂
