You can use the lsb_release command to determine what version of Ubuntu you're running.
Open a Terminal window or connect to your workstation via SSH, and execute the following command:
The command should display something like "Ubuntu 10.04 LTS".
If there is more than one decimal point in the number, disregard everything after the second decimal point. For example, if the command returns "Ubuntu 10.04.2 LTS", you are running "Ubuntu 10.04".
Ubuntu versions are also often referred to be their codenames (e.g. Ubuntu 12.04 has the codename "Precise Pangolin" and is shortened to "precise").
You can see the codename of your distribution with this option to the lsb_release command: