You added some junk to your software sources (tuxfamily.org is not part of a standard Ubuntu install, and Feisty is an old release that's no longer supported). Why did you add this software source? Whoever gave you this bad advice should now help you solve the problem (in my opinion).
If that doesn't work, my suggestion is:
Find the line containing http://download.tuxfamily.org and type a # symbol at the beginning of the line (to "comment it out" so that it's skipped). Then save the file and try your upgrade again.
gksu gedit /etc/apt/sources.list
If you've added this software source for a specific reason, you need to be clear why, so we can help you.