Featured Image Huge on Homepage

Please help. On my blog homepage, the featured images used to be a thumbnail size and perfect. After the last update, the featured image photos are HUGE! and I cannot find how to make them smaller. Per wordpress advice I used a regenerate thumbnail plug-in to no avail. Please advise on how to reduce the size of featured image on blog home page. I am not using featured image now because the image was takingup half the page but it needs corrected.