Spacing out images?

In the Gallery Settings page, I have set the number of columns to display to 5. What I want to do is space the columns out across the space so there is a gap and all the images are not cluttered on the left hand side of the page.

My website is

I am sure I have done this before but I have made changes and can’t figure out how you do it? Does anyone have any hints ?

http://wordpress.org/plugins/nextgen-gallery/