When installing Revit, various libraries can be selected, which are downloaded and made available during the installation process. If the Internet connection is not stable or you want to download content afterwards, this is very easy via the Control Panel > Change or uninstall programs > simply search for Revit Content Libraries and start the setup.
About Add or remove functions you can select or deselect the library again:
Tip: Did you know that you can download the new German-language Revit content, which is only available with Revit 2019, for the 2018 version? here can download? 😉