Change the gallery layout

You can change the image gallery layout by doing the following:

Go to the Admin Panel > Image gallery (any one) > Advanced

Scroll down, and click on Advanced Layout Options or click on one of the layout suggestion icons.

Clicking the layout suggestion icons will automatically select the layout options. 

Gallery layout options are as follows:
Can I change the layout for all galleries at once?
Yes.  Once you have set the layout options that you want, be sure that the Apply above changes to all image galleries option is checked.

And, click Save Changes at the bottom.

How can I quickly preview the recommended gallery layout options?
Try the layout tab.