Stop Item Images from Scrolling

[GXP]

I’ve seen several threads on this with no clear answer.

When I upload an image for an item, it becomes the main image for that item.

If I upload additional photos to the same item, it chooses a random image (from those that have been uploaded) as the item’s main image, each time the store page loads up.

How can I upload multiple images of an item and choose only one of those images to always be the main item image?