How to add your image to the link in the body of the post?

Question

Facebook

The essence is this (public post):
I insert text with a link into the body, then FB loads the picture (s) from the page to which the link goes.
In front of me I see a slider of pictures (in my case 5 pcs) that FB loaded from the page.
Everything seems to be nothing, I wanted to put a picture (one) of my own, there is a button for uploading, I upload it.
I see it in preview mode, I try to select it, and then a bummer - FB resets it to the default image, which (s) he loaded himself.
If I upload my pictures from 2 or more, I can choose, but I don’t give one, although I can put one, but from those that FB uploaded.
What can be wrong?