Parquetry main graphic

I am using the Parquetry theme, and have got everything going smoothly except how to change the main graphic image on the theme. I have some ideas to play around with, but wondering if someone knows how and can tell me how to change it easily. All the other WP themes I used it was easy to select featured images for the theme, but this appears to need to be changed in the html in the style page? thank you