Hi,

First I would suggest you to enable the Elementor post type for Portfolio, so go to Elementor > Settings and tick on the Portfolio box.

- https://prnt.sc/r269dx

After that a button at the top of portfolio item will appear that says 'Edit with Elementor', start edit the portfolio with Elementor and you'll be able to change images and all the stuff.

You can also use the navigator for easier orientation.

Navigator: https://docs.elementor.com/article/378-navigator

Feel free to ask for anything you need.

Kind Regards