Center images

Hi, I love the simplicity of the gallery just one tiny problem I would like 4 columns per row (I’m using the lite version) and it looks like my thumbnails are too big, which is the ‘perfect size’ for thumbnail to sit 4 in one row? and how to center them, on my site they are aligned on the right right, please note I don’t know to create code for centering pics 🙁 I just want to center them.

Thanks for your help.

http://wordpress.org/plugins/maxgalleria-lite/