If you have root-level access to a hosting server, this means that you'll have full control over it. That is to say, you'll be able install any server-side app irrespective of the changes that it'll make to the software setting on your server, and you will be able to both access and update any kind of file, including system files, and modify any settings. You can do this by connecting to the server as a root user which has full privileges to do the aforementioned things as well as to generate other users, including users who also have full privileges. This particular can be established using a web-based graphical interface or a Secure Shell console. For safety reasons, it's recommended that you make a separate user for your everyday work and employ the root user only when you have to modify the server or to install software which may be needed by a script-driven app that you would like to run.