If you have root-level access to a hosting server, this means that you will have full control of it. In other words, you can install any server-side app whatever the changes that it will make to the software setting on the server, and you'll be able to both access and update any kind of file, which includes system files, and modify any settings. You can do this by connecting to the server as a root user who has full privileges to do the aforementioned things and to generate other users, which includes 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 is recommended that you create another user for your everyday work and employ the root user only when you need to customize the server or to install software which may be needed by a script-driven application that you want to run.