You can use the following custom css to center your footer content on an OptimizePress LiveEditor page:
Add this code in the Page Settings > Other Scripts > Custom CSS section
.footer-navigation {float:none;}
.footer-copyright {float:none;padding-top:5px;}
.op-promote {float:none;padding-top:5px;}
This will center any footer navigation, the footer copyright and footer promotional tag if you have it enabled. It will also add a little padding to the top of some of the elements to allow them to be evenly spaced.