Code for gallery forward/reverse buttons?

I am using the Category Grid View Gallery plugin.
http://dstollart.thatiam-online.com/

When clicking on an image in the gallery, lightbox opens to show the post associated with the clicked image. From there, you have to close the lightbox in order to change posts. I have thought I would try to add code to the plugin to give > and < arrows and functionality so as to be able to advance through the gallery items without have to close and re-open the lightbox. Of course, since the items are posts and not images this may be more difficult than I think. But I would still like to try.

Does anyone have a viable code snippet that I could start with for this purpose? And a few hints regarding where I should place it, how to call it, whatever is needed to use it, etc.

Thank you!