HTML blog images

I am a paid customer.

I have created a blog post using HTML builder. It works good enough for me however the issues I am having is this.

I go into the templates and ad my own images but they do not stay once exported and uploaded to my site.
See attached "template-save" how it looks with my image saved then exported.
"template-upload" how it looks after uploading and viewing on website live.

I am not sure how your template decides what image it chooses when you do a new post. I want to be able to change images for every new post, is this possible and how do we do it please?

thanks
Paul