The default installation of Ubuntu Oneiric doesn’t come with any option to configure the Unity desktop. You can, however, install CompizConfig Settings Manager to access the configuration menu.
sudo apt-get install compizconfig-settings-manager
Once installed, run the app and scroll down the list till you see the Ubuntu Unity Plugin. Click on it. From here, you can configure the behaviour of the launcher, the shortcut key, the switcher and some experimental features.
If you need help using CCSM read this post
If you are using an old computer that doesn’t support Compiz, most probably you are running Unity 2D instead of the usual Unity desktop. To configure Unity 2D, you have to install dconf-tools using the following command in the terminal:
sudo apt-get install dconf-tools
Next, in the terminal, type:
Navigate to Desktop -> Unity. You can find several configuration options here.