1) Regarding the portfolio plugin, yes it’s installed because it’s developed by Creiden and it’s packaged with the theme, if you would like to use it just activate it, it’s disabled by default in case you don’t have portfolio.
Portfolio is not related to the slider.
2) I see you mean the sections background images, they are easily editable through the page builder
When you edit the column block you will find the background options, feel free to edit:
I have edited them now for you, and added the exact images used in the demo, feel free to edit.
By the way we just import random background images in the demos, that’s why.