To use any of these functions, your SonarQube server will have to have access to the internetrequire an Internet access. To take effect, most actions taken in the Update Center (updating a plugin...) will require SonarQube to be restarted. The Update Center is only accessible to System Administratorsadministrators: Settings > System > Update Center.
If your server has no access to the internet, then you won't be able to rely on the Update Center for plugins, and will have to handle plugin installations and upgrades manually.
To know what plugins are available and which version of a plugin is appropriate for your server, use the plugin version matrix, which is kept up to date with plugin availability and compatibility.
To install a plugin, simply download it using the manual download link on the plugin documentation page, place it in [sonarqube-home]/extensions/downloads, and restart the server.
perform your plugin upgrades manually.