Could not download the upgrades The upgrade has aborted. Please check your Internet connection or installation media and try again. All files downloaded so far are kept.

You strictly need to open a Terminal from the menu Applications->Accessories->Terminal and type:

sudo dpkg --configure -a
sudo apt-get -f install
sudo apt-get --fix-missing install
sudo apt-get update

give your user password when requested, you don't see nothing when you type it, then press enter.

I had the same problem and then i just changed the server from which the computer downloads the updates.
To do that open the update manager, and in the bottom left corner there is a button that says "Settings". Click it and in the first tab called "Ubuntu Software", there is a select element called "Download from". Select another server, close the window and try to upgrade again.