space between images

I can’t figure out how to remove space between images.
When I upload images and use them for the first time (and when I imported posts from blogger), I could remove space between images no problem.

However, I try to use them again (as I don’t know how to re-order images), there’s a space I can’t remove.

Also, is it possible to re-order images after adding to the post?

Thank you

Update : I kind of find out.

When I set image Align “Center”, the space appeared, and set Align “None”, the space is gone.
That’s how it works?

I can’t tell the difference between “center” and “none” though. It seems same in a post?