Can I change the photos/thumbnails on my gallery index page?

As the title says, can I change the thumbnail photos on my gallery index page? It's been a long time since I created my website and I've forgotten how I did most of it. It appears that the gallery index thumbnails are thumbnails of the banner photos I've used for each gallery, however they're massively cropped and not full images. Ideally I'd like to have full images for the thumbnails rather than the crops that chop a lot of the photos off. 

Any help would be appreciated.

Gallery index thumbnails 

Gallery banner for landscapes and cityscapes

Hi,

What is site url?

1 hour ago, tuanphan said:

Hi,

What is site url?

Sorry it should be listed as I did fill that part in. It's 

http://www.tobygunneephotography.com/gallery-index

On 2/17/2023 at 6:22 PM, snerkler said:

Sorry it should be listed as I did fill that part in. It's 

http://www.tobygunneephotography.com/gallery-index

Thank you. You mean make these images doesn't crop?

On 2/20/2023 at 3:15 PM, tuanphan said:

Thank you. You mean make these images doesn't crop?

Yeah, I want them to be full images and not crops but there doesn’t appear to be any option to change them, it appears that they’re automatically taken from the banners of the main gallery pages. 

20 hours ago, derricksrandomviews said:

The thumbnails in a Montauk index page come from first image in each gallery, and you can't really adjust the crop, just as in Avenue. You can adjust the following: 

• Choose how many thumbnails display horizontally with Thumbnails per row.
• Set the height of the thumbnail images with Thumbnail ratio.

Ahh ok, thanks. That’s a shame. 

I should explain that if you want to change the thumbnail image, I think you rotate the order of the images  by editing the media content. That is the way my index pages work in Avenue.