Hi Sansal. You'll need to run Notepad (or whatever editor you'd like) as Administrator. It's not quite the same as changing security permissions on the file, which you've already tried. The application itself needs the high privileges -- not the file. Find Notepad in your Start Menu, right-click it and choose "Run as administrator". Then open the file using the File menu, edit the file and save it. You'll then need to go into Local Services, find the odoo-server-8 service and restart it before your changes will take effect.

I hope this helps!