Help with image sizing please!

Hey everyone, I’m using Divi, and have multiple image galleries throughout my site.

The problem is, the images all apear different sizes!

here’s the page Im trying to fix at the moment…

https://www.decoratethetable.com/knowledge-base/

How can I make all the images neat and the same size like the demo here – https://www.elegantthemes.com/preview/Divi/image-gallery/

Thanks very much in advance!

Alex