firstly... yo get from the comand prompt to the gui and back afaing... hit ctrl + alt + F7 (gui) or ctrl +alt + F1 (command prompt) [ctrl + alt + F1 through to F5 all have seperate command prompts... like virtual desktops ... but older!]
getting yop the file... type
your now in the /etc (configuration and settings) directory....
to edit the file... type
that should bring up a prity easy to use text editor.
after that my experteese runs out im afraid