Hi @leuchterits ,
Thanks a lot for getting back to me.
You do not need to change anything on your ACF front-end form if its still saving as expected. What you need is to hook into the acf/save_post as described earlier.
From here you can now call the native WordPress function wp_create_user() to create a user using the field values. https://codex.wordpress.org/Function_Reference/wp_create_user
If you get stuck along the way, feel free to share with us a gist of your code and we will try to help 🙂
