Unable to change photo on front page

I suspect this is a stupid newbie question.

I had HighEnd installed for me by Mojo Marketplace. The service included having the theme installed to look like the demo.

I thought I’d be able to replace the photos on the home page with my own. After days of trying to figure out why I’m not able to, it has finally dawned on me that having the demo theme is probably the problem.

If so, how can I go back the version of the theme that lets me put my own product photos on the front page?

Thank you