How to add additional side to my slide show.

Hi everyone.
I am having a problem with our company webpage:
https://www.spszansa.pl

When you enter a webpage one the main page you can see a slideshow box that contains 6 pictures. They change automatically. There is also a small box (similar) at the bottom.

What I would like to do is to add additional pictures to the slideshow so that the total number would be 9 or 10.
It is a custom theme (that was not made by me) and I simply cannot find a way to do it.
Is there a way to alter the theme or anything else so that it would display more than 6 photos. Thanks.