Hello,

that's actually the hero subtitle (which is part of the top 'hero section')

Editing the theme is fairly easy: you have the portfolio items (under admin -> portfolio) and normal pages with options and content. The most important portfolio options are the hero image and captions (title and subtitles). The content can be edited as in normal pages, there is nothing special about it.

You can access the page & portfolio item options by clicking 'Edit' (not 'Edit with Elementor') and then scroll past the editor area to get to the options panel. Click on the Hero Section tab to activate it. You can change there the hero image, title and subtitle.