Image banner not responsive.

Hi, i hope everything is going well. I contact you because i have a problem with the image banner. I realised that when i open it in a movile or tablet, the text is responsive but the image isn’t. I leave you an example of your web of what i’m speaking about. And i leave you as well my screenshot.

I attach you also the screenshot of the flipboxes, beacuse they do well the responsive, and is how i want to put the image banner.

Sorry for my english, i hope you can understand me, i do it the best i can. ^^
Thank you a lot!