To change the theme in Ubuntu 16.04 or 17.10, you can use the Unity Tweak Tool. This tool allows you to customize various aspects of the desktop environment, including the theme.
To install the Unity Tweak Tool, open a terminal and enter the following command:
sudo apt-get install unity-tweak-tool
Once the Unity Tweak Tool is installed, you can launch it from the Dash by searching for "Unity Tweak Tool".
In the Unity Tweak Tool, click on the "Appearance" category in the left sidebar. In the "Themes" section, you will see a list of available themes. To change the theme, simply click on the theme that you want to use.
You can also use the Unity Tweak Tool to customize other aspects of the desktop environment, such as the icons, cursor, and fonts.
Alternatively, you can use the Gnome Tweak Tool to customize the theme in Ubuntu 16.04 or 17.10. The Gnome Tweak Tool provides more advanced customization options and allows you to change the theme for the Gnome Shell interface. To install the Gnome Tweak Tool, enter the following command in a terminal:
sudo apt-get install gnome-tweak-tool
Once the Gnome Tweak Tool is installed, you can launch it from the Dash by searching for "Gnome Tweak Tool". In the Gnome Tweak Tool, click on the "Appearance" category in the left sidebar. In the "Themes" section, you will see a list of available themes. To change the theme, simply click on the theme that you want to use.