I hope this comprehensive guide helps:
How to edit the Social Media Icons and links1. Go to Design/Blocks
2. Edit the Social Icons block
3. Add your HTML line such as <a href="
http://www.facebook.com/AbanteCart" target="_blank" title="Facebook" class="facebook">Facebook</a> and Save
4. Open the icons grid from /Storefront/View/Default/Image/Footericon.png
5. Erase over one of the unused icons such as Dig or Linkedin
6. Download your new icon from the internet (i.e the F for Facebook) and put it in the spaces you just made (you need to add it to the top and bottom grid as the bottom grid is a Hover icon)
7. Use the Photoshop filter to select a Colour Overlay to match the top and bottom grid
8. Save the image
9. Open /Storefront/View/Default/Stylesheet/Style.CSS
10. Find references to the inage you just erased (i.e Dig) and change the word in 4 places from Dig to Facebook (or whatever icon you just added) then Save
11. Put all of these files back on your FTP server and BINGO!