Try these steps, from the command line:
Fix broken dependencies:
$ sudo apt-get install -f
If it still doesn't work, try this to fix/reconfigure the existing, unpacked-but-not-yet-configured packages:
$ sudo dpkg --configure -a
Then try the upgrade again.
If it fails again, you may want to delete all the already- downloaded packages (they should be stored in
$ sudo apt-get clean
That will clean up the packages but if you're still stuck in some weird state, I'm not sure what else to suggest.
$ sudo apt-get autoremove -y
That will remove any now obsolete packages.
Of course, before you do anything you should back up any important contents of your
/home/dave directory (or whatever your
$HOME directory is).