How to delete a banner?

Complete noob, learning as I go, and trying to decipher a charity website originally set up by someone else.

I need to delete an outdated banner from the very top of the home page and can’t find where or how it’s been created. I’ve searched the whole of the dashboard in vain.

The theme is Minamaze (Pro). The dashboard says there are no widgets active.

The page I need help with: [log in to see the link]