Can't modify the thumbnails

I’m now using the plugin Gallery from BestWebSoft combined with Responsive Child Theme.
But the pluging doesn’t satisfy me, because I can’t change it, the way I like it to be..
The plugin gives to much space between the thumbnails. (http://www.studionoordster.com)

What I want is to have my thumbnails with just a small border (1px) among each other or maybe not even with a border.

http://wordpress.org/extend/plugins/gallery-plugin/