How to create image swap gallery

Hello – I would like to create a gallery like this one: https://www.johnrichard.com/new/room_scenes.asp

If it could connect to NexGen gallery that would be terrific, but I don’t mind plugging in names of images either.

I see some posts about image swap, etc. but I can’t exactly get to the bottom of how to do it. (Medium tech abilities…)
Thanks in advance!
My site: https://nicolehoughdesigns.com