your theme seems to be using a grid system layout for css (bootstrap) and it's assigned a 3 column layout for the footer. i've not used bootstrap so i can't really tell you where you need to go exactly but my guess would be the footer.php file, find instances of .col-md-4 and change that to .col.md-3 and that should give you 4 columns in the footer.
all your columns should add up to 12 (3x4 = 12 etc)
hope that helps a little bit.