[Sugar and Spice Theme] How to set full size featured image on homepage

Hi guys..i need to show my feature image in full size 700px x 366px height on my homepage, instead of 210px x 210px as the theme default size.

I have try to change the set_post_thumbnail( 700, 366, true), but won’t change anything. Using code .blog attachment-post-thumbnail to required size making it show hardly stretch and ugly.

Thanks for your attention