Gallery visualization pronlem

hi everybody, sorry if my question could sound trivial to many of you.
I have problem with a wp-theme (and the author didn’t help me so much). The img gallery slider doesn’t work properly. it always show images in just one size stretching them when they are of different proportion of the box.

here’s the link where you can see what i mean

https://www.b01arquitectes.com/arc_project/el-semafor/

thank you