Update:

sudo apt-get update        # Fetches the list of available updates
sudo apt-get upgrade       # Strictly upgrades the current packages
sudo apt-get dist-upgrade  # Installs updates (new ones)

Clean up the system from old packages:

sudo apt-get update && sudo apt-get autoclean && sudo apt-get clean && sudo apt-get autoremove

Check the Ubuntu version:

lsb_release -a