Uninstall mongoDB from ubuntu

I have installed MongoDB 3.0.1 following the commands in [Install MongoDB Community Edition on Ubuntu][1] on my ubuntu 14.04 64 bit system and I installed [Robomongo][2] interface to use that. When I try to connect MongoDB using Robomongo I get an error that authorization failed. I found [Add support for SCRAM-SHA-1 authentication (MongoDB 3.0+)][3] which explains that Robomongo 0.8.5 doesn't support MongoDB 3.0.X fully. In response, I want to remove MongoDB 3.0.1 and install MongoDB 2.2. I tried the following commands: apt-get remove --purge mongodb and also apt-get autoremove --purge mongodb In both cases I got the following error: >" Could not open lock file /var/lib/dpkg/lock - open (13: Permission denied) E: Unable to lock the administration directory (/var/lib/dpkg/), are you root?" Any help would be appreciated. [1]: http://docs.mongodb.org/manual/tutorial/install-mongodb-on-ubuntu/ [2]: https://robomongo.org/ [3]: https://github.com/paralect/robomongo/issues/766