Unable to remove directories on uninstall

Due to some difficulties, I never installed Piwik after I uploaded it onto my site. I never made a database after I was prompted to do so and just decided to tackle this another time, so I tried to “uninstall” Piwik by deleting the entire directory off my site via FTP.

But I’m encountering errors deleting several folders off the site, and I keep getting the error in the screenshot attached. The folders I have left that refuse to be removed are config, core, js, lang, libs, plugins, themes, and tmp, and get the same error when trying to delete each of the folders.

Any suggestions?