$ sudo sed -i 's/saucy/trusty/' /etc/apt/sources.list

$ sudo sed -i 's/petra/qiana/' /etc/apt/sources.list

$ sudo sed -i 's/saucy/trusty/' /etc/apt/sources.list.d/official-package-repositories.list

$ sudo sed -i 's/petra/qiana/' /etc/apt/sources.list.d/official-package-repositories.list

$ sudo apt-get update && sudo apt-get dist-upgrade

$ sudo apt-get upgrade

$ sudo sed -i 's/saucy/trusty/' /etc/apt/sources.list

$ sudo sed -i 's/petra/qiana/' /etc/apt/sources.list

$ sudo sed -i 's/saucy/trusty/' /etc/apt/sources.list.d/official-package-repositories.list

$ sudo sed -i 's/petra/qiana/' /etc/apt/sources.list.d/official-package-repositories.list

Use sed to replace references to saucy with trusty, and petra with qiana in the sources

$ sudo apt-get update && sudo apt-get dist-upgrade

$ sudo apt-get upgrade

Update the repositories with the new settings and run a dist-upgrade to upgrade to the new version cleanly, then run upgrade to make sure all the packages are updated.