home page thumbnail images change but not blocks

how do i change my home page thumbnail image size currently it’s shows me 200 x 200 whereas i want to do 150 x 150 whereas i try to functions.php and changed this line add_image_size(‘article-thumb’, 200, 200, true); but after i made 150 150 then my image block 200 x 200 and image 150 x 150 so i reset all things now please let me know how do change image 150 x 150 and block as well

http://www.unlimitedtrading.biz/