[Theme Horse Support Team]

Hi Michael,
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. So better make child theme and first unhook the functions and the edit the code.

http://codex.wordpress.org/Child_Themes

You can change it from your theme folder -> functions.php
Can you see this line
add_image_size( 'featured', 670, 300, true );

670 and 300 is your width and height of image if you upload more than 670 width and 300 height. So you can change this 670 to any you want and 300 to any height you want.

Thank you!