Opencart usually doesn't use newest fontawesome version or you are using old opencart version. This tutorial will help you upgrade newest fontawesome version for your site
Firstly go to and download newest version of Font-Awesome
http://fortawesome.github.io/Font-Awesome/
- Unzip the file just downloaded you will see folder font-awesome-xxx with xxx is version for font awesome.
- Click open that folder and upload all files and folder to catalog/view/javascript/font-awesome
Done!
how to upgrade newest fontawesome version to opencart