upgrade Mint Linux 11 to Mint linux 12 rc.

Go to your /etc/apt/sources.list

Open “source.list in a text editor as admin or root privilege.

Change the OS’ codename (in this case, “katya” to the mint 12 codename ” lisa”).

Change the codename “natty” to the ” oneiric”.

Then type in terminal “apt-get update” and then “apt-get dist-upgrade”.

To install gnome-shell, after upgrade install “gnome or gnome-shell from package manger.

Source.list file final look.

deb http://packages.linuxmint.com/ lisa main upstream import romeo backport
deb-src http://packages.linuxmint.com/ lisa main upstream import romeo backport #Added by software-properties

deb http://archive.ubuntu.com/ubuntu/ oneiric main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ oneiric-updates main restricted universe multiverse
deb http://security.ubuntu.com/ubuntu/ oneiric-security main restricted universe multiverse
deb http://archive.canonical.com/ubuntu/ oneiric partner
deb http://extras.ubuntu.com/ubuntu oneiric main
deb http://packages.medibuntu.org/ oneiric free non-free

Note: Some cases, upgrade may break. so please backup files before update.