Hi nsleeth,
Go to theme folder -> functions.php on line no 142 you will see this code add_image_size( 'slider-wide', 1400, 460, true ); and replace it with add_image_size( 'slider-wide', 1400, 700, true );
We recommended not to change the code because if you change the code then while updating to our new version all your customisation code will be lost. if you wish to add new slider then same customization is required. So better make child theme and customize the code.
http://codex.wordpress.org/Child_Themes
After the change is made on image size use regenerate thumbnailsls plugins to regenerate the images.
Thank you!
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