You are most welcome.
As advised by Esmi – for minor CSS modifications please use the referenced plugins list.
For major CSS and PHP/HTML modifications please refer to the link provided above and use a child theme. For a starter StrapVert child theme please refer to the FAQ at: http://www.wpstrapcode.com/faqs/my-child-theme-does-not-work to get a copy.
In in response to your question – you’ll need to copy footer.php in to your child theme and then edit that.
Regards,
Zulf