it’s located here
http://comobajardepesoya.com/wp-content/themes/amazing-grace/images/bg-portrait0.jpg
easiest thing to do would be create new image and name it same as old image
rename or delete old image
upload new image to same place
I assume you mean the image with the tape bearing the number 8? If so that image is located at wp-content/themes/amazing-grace/images/bg-portrait2.jpg or in this case comobajardepesoya.com/wp-content/themes/amazing-grace/images/bg-portrait2.jpg
You’ll need an image editor to get it to look right.
Quick Draw McGraw beat me to it. 😉
Looks like the theme is using a image rotator of some sort and can tell you where to change images and there might few images there in images folder
wp-content/themes/amazing-grace/images/bg-portrait3.jpg
so you can change those images keeping same size and same name.
they may be named bg-portrait 1 2 3