Make sure your mirror is set to the "official" one
To open a terminal window hit the "Ctrl" and "Alt" keys, and the letter "T" key.
The command prompt lines are
sudo apt-get clean
sudo apt-get autoclean
sudo apt-get update
sudo apt-get dist-upgrade
Type "Y" when prompted
Then click enter
Then "y"
Store/bookmark/save for future reference
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