When a file is owned by the root user, the first thing you will see is a padlock on the file.
You can check the permissions of the file by right clicking on it, clicking properties and then clicking the permissions tab. As you can see ownership of the file belongs to the root user. If we want to be able to write to this file, then we need to change the ownership of this file to our own username.
To achieve this open your terminal and enter the following command, you will be required to enter your password