There are two ways to check which version of Ubuntu you are using: through the system menu or through the Terminal. The way through the system menu depends on which Ubuntu version and desktop environment you are using. The way through the Terminal will work no matter what you are using.
Through the System Menu
This method depends on your version of Ubuntu and whether you are using the Unity or Gnome desktop environment. These methods might not work if you are running an Ubuntu derivative such as Kubuntu, Xubuntu or Lubuntu.
Unity is the default desktop environment for Ubuntu 11.04 (Natty Narwhal) and later.
- Open your System Settings
- Select either System Info (for version 11.10) or Details (for versions 12.04 and 12.10)
- Find your version of Ubuntu in the Overview section.
Gnome is the optional Classic Desktop Environment for Ubuntu 11.04 (Natty Narwhal) and later, and the default desktop environment for earlier releases.
Your Ubuntu version can be found in two places:
- Under System > About Ubuntu
- On the System tab of System Monitor (System > Administration > System Monitor)
Check the list of Ubuntu versions to see when your version was released and if an upgrade is available.
Through the Terminal
This method will work no matter which version of Ubuntu or desktop environment you are running.
- Open the Terminal (keyboard shortcut: Ctrl+Alt+T)
- Enter the command lsb_release -a
CheckingYourUbuntuVersion - Community Ubuntu Documentation