Environment files allow you to configure global variables, specific to your website. It is easier to keep things like public keys, and specific URLs in one place, and this is what environment files are for.
environment.ts - used for development, by default environment.prod.ts - used for production, by default
Images can be changed with the website repository. In the
assets/img directory, all you need to do is replace the image content, while keeping the file names the same.
By default, the website uses the Next Gen theme. The process is the same as 2PG, as both website projects are quite similar. Make sure to edit the CSS variables to match your preferences.