Please be aware the theme does not have an option to change the image sizes for blog post images and its recommended to use landscape image so the theme could crop them properly. However image sized could be changes through source files and these changes totally deal with customization. Unfortunately we do not provide our customers with any custom work due to our policy. We only do Support for our products if there are some issues in work, or some elements cause issues, etc.
In case you need to make some customizations you could try to figure this out on your own, which needs some skills in coding and programming.
In case if you believe our theme misses enough custom options to fully meet your needs you could involve/ask for help a third part developer to customize the theme the way you personally like.
Thanks for understandings and sorry for any inconveniences!