I was just trying out the Commerce feature and added an item for purchase.

 

I can see a placeholder image for this item and a "Product information" section. However I can figure out how to modify these two things.

Is it in a different location in ACP?

The "Product Information" is the "Description" on the Store Settings tab:

 

Then the "Images" field underneath are the images that show there.

 

You can read more about setting up Products in this guide: 

 

OMG I think I need a nap. I was looking all over, and honestly couldn't find it. Thank you!

You're very welcome! Glad we could be of assistance.