To completely remove the OpenGeo Suite, use:
sudo apt-get --purge remove opengeo-suite
on the command line. I don't think Ubuntu 12.04 is officially supported by the OpenGeo Suite. You'd be better off using an older version. Or a VM if all you want to do is test it.
Smaran - here's how I managed to get this done. As jdeolive points out, this is unsupported, and I cannot vouch for how the heck I got this to work. I haven't done a ton of troubleshooting, so it's not really ready for primetime.
I'm making the assumption that you're trying to run the latest versions of various software, like Postgres & PostGIS, etc. Key note: just because you can get all of these packages to install happily together doesn't necessarily mean they've been tested or will work well together.
Steps
Install Postgres 9.1 & PostGIS 2.0 on this page: trac dot osgeo dot org/postgis/wiki/UsersWikiPostGIS20Ubuntu1204
Install the latest version of geonode following instructions at:
geonode dot org
Follow the steps below to set up an equivs package for libgdal.
Add the opengeo repository info to your /etc/apt/sources.list file.
sudo apt-get update
sudo apt-get install opengeo-suite
Equivs Setup
The lone dependency breaking opengeo-suite right now appears to be libgdal. Ubuntu and Debian have typically called this libgdal1, for whatever reason. So, you need to trick apt into thinking libgdal is already installed. You can do this using something called equivs.
# sudo apt-get install equivs
# equivs-control libgdal
then, edit the file 'libgdal' to look something like this: http://pastebin.com/bGUa5BiP
# sudo equivs-build libgdal
# sudo dpkg -i libgdal_1.9.1_amd64.deb
Like I mentioned... there are a few items I've skipped here, like adding java support for PostGIS and /usr/lib/gdal.jar, etc., but I think you may be able to figure those out. Please add what info you can here.
Best Answer
Actually on Linux installations the postgis specific functionality on the dashboard is explicitly disabled since it's not running as a native app. So unless you saw some installation errors it is probably fine. You can verify by logging into the database from the terminal. Try this.
psql -U opengeo medford select postgis_version();
If that all works everything should be fine.