You can also disable Lightbox from being used entirely, by removing its script request from the showflat template. This will affect all of your posts, including your galleries/gallery posts.
FIND AND REMOVE THIS LINE:
(it is toward the end of the template)
CODE MODIFICATION DISCLAIMER:
// You may make modifications, but only for your own use
// and within the confines of the UBB.threads License
// Agreement (https://www.ubbcentral.com/terms.php
// Note: If you modify ANY code within your UBB.threads,
// we at UBB Systems cannot offer you support.
// Thus, modify at your own peril