What's left aligned? Is it the slideshow itself, and/or the text in the descriptions?
To center the slideshow, just wrap it in a div that's set to the same width as it is and set that wrapper div's style margin to 0 auto. For example, on the included demo.htm file, for the first slideshow:
Make that like:
That will take care of things for most situations. However, your layout might vary. If that's what you're going for (centering the entire slide show) and the above doesn't work for you, give me a link to the page so I can see what we're dealing with.
<div style="width: 350px; margin: 0 auto;">
If you just want to or also want to center the text in the descriptions, add this to the stylesheet:
That's about it.
text-align: center !important;
If you want more help, please include a link to the page on your site that contains the problematic code so we can check it out.