Editing footer in Twenty Thirteen Theme?

I just posted this in the “Fixing WordPress” forum, but not sure if I’m able to move it to this forum or of this forum is the correct location for this question – so apologies in advance if I should not be re-posting this here.

I recently updated the Twenty Thirteen theme on a self-hosted WordPress installation to v3.7, and in doing so accidentally lost changes I had made to the footer. I think I had previously implemented these changes by editing the footer.php file (under wp-content/themes/twentythirteen), but when I tried to mimic these edits in the footer.php now, the changes aren’t showing up on the website. Am I doing something wrong? Did WordPress change how the footer works in the current version of the theme? Any help is greatly appreciated – thanks!