Ubuntu – Upgrading from ubuntu 12.04 LTS to lubuntu 14.04 lts

Execute these commands:

sudo apt-get autoremove lxde
sudo apt-get autoremove lubuntu-desktop
sudo apt-get --purge remove lxde
sudo apt-get --purge remove lubuntu-desktop

_{Note: it would be possible that lubuntu-desktop packages may not be installed.}

Also execute this command to get the packages of lubuntu-desktop:

whereis lxde

You would get the path like /usr/share/lxde

Remove the directory /usr/share/lxde completely by:

sudo rm -rf /usr/share/lxde

Since I mentioned the commands in one line that would be the problem. Try it once. I'm also listing my output of the first command:

sk@sk-Vostro-1015:~/.config/openbox$ sudo apt-get autoremove lxde
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages will be REMOVED:
  galculator giblib1 leafpad libxmmsclient-glib1 libxmmsclient6 lxappearance lxde lxinput lxmusic lxrandr lxsession-edit menu-xdg scrot xmms2-core
  xmms2-plugin-alsa xmms2-plugin-id3v2 xmms2-plugin-mad xmms2-plugin-vorbis
0 upgraded, 0 newly installed, 18 to remove and 56 not upgraded.
After this operation, 7,384 kB disk space will be freed.
Do you want to continue [Y/n]? 

Reply if you get any problem :)

Until about April 2017, yes: https://wiki.ubuntu.com/Releases. LTS releases are supported for 5 years. However, the longer you stick with Ubuntu 12.04, the harder it will be to migrate. Things may have changed drastically in 5 years (just compare 8.04 and 12.04). I recommend that you upgrade next year, when 15.04 is out. A year's time should be enough for you to check on compatibility, and barring proprietary drivers and associated problems, 14.04 will run on most about anything that can run 12.04.