Sometimes there are cases that after you update css and js files some users may not be able to see the changes because their browsers use cached versions of these files. An experienced user will just reload a page without cache, but if you want to help other users you can try this free module: “Manual version for JS and CSS files”. The module adds a line into the source code where indicating version of the file. For example: “http://belvg.info/demo/prestashop/facebook_all_15/themes/default/css/grid_prestashop.css?version=17”
With a manual indication of the current file version in the admin you can force browsers to reload content.