If you have root-level access to a server, it means that you will have full control of it. In other words, you can install any server-side application regardless of the changes that it will make to the software environment on your server, and you'll be able to both access and change any file, including system files, and modify various settings. You can do this by connecting to the server as a root user that has full privileges to do all these things and to create other users, which includes users who also have full privileges. This particular can be established through a web-based graphical interface or a Secure Shell console. For safety reasons, it is recommended that you create one more user for your everyday work and use the root user only when you have to modify the server or to set up software that may be needed by some script-driven app that you wish to run.