I downloaded the Faenza icon theme. I also installed the Advanced Settings app from the Software Centre. I double-clicked the Faenza install file and it opened a Terminal list of commands which I followed. Easy enough. Except that I noticed that you're supposed to install it as Root (so that it can copy the icon files into the file system rather than Home. If you don't install as Root, then a bunch of the icons aren't copied across.
This meant that it installed twice, as you can by the screenshot.
I simply want to remove the non-Root files but don't know where they copied to. Does anyone know where they would be?
Gonzozo solved the problem in a comment: