Pinboard Theme – Slider Images – Different Sizes

Hello! I’m just wondering how I can have all the images on my slider be the same size. I tried changing all the featured images to 1140 x 395 px but to no avail. Some are big and some are small. I’m not too techy, and I really wouldn’t know how to change the codes and all. What can I do to fix this problem? Thank you so much.

Mary

PS:

Here are screenshots

https://i.snag.gy/aNGsU.jpg — small size

https://snag.gy/S9U6m.jpg — some slides are big

I hope you can help me. Thanks in advance.