How to edit a file in Program Files
Windows User Account Control (UAC) is a security infrastructure introduced with Windows Vista and has been included in all Windows versions after that so far. UAC limits the access to application software to ensure that they cannot perform actions that might harm the system in any way.
Because of how UAC works you might have noticed a few times that you are unable to edit specific files, getting an access denied error. The reason for that, as stated above, is because UAC is limiting the access you have to particular folders and files, allowing you in most cases just to view them.
In order to be able to edit a file that is protected by UAC you will need to access that file while having administrator rights. Luckily there is an easy functionality provided by Microsoft for that. Right click the application, file or folder you want to run as administrator and select the Run as administrator option.
That will give administration rights to the program/file you want to run, allowing you to modify the contents where in other cases would be impossible because of UAC.