PLEASE help: CORE Theme photo size

I am looking for some “basic” help. I purchased the CORE template for WP. I purchased photo’s licensed by Fotolia and, purchased photo’s that are too large for the theme. I shrunk the size using Photoshop, however, the photo’s are still not loading. The template says the optimal size is 64MB, some of my pics are only 787 KB. Any advice? I am not very technical and would appreciate a very elementary response.