Never had to do one, myself.
All I'd do is have a GOOD look at how it is fitted, where it runs and then have a bash at replacing it myself.
Do one end at a time (probably start at the engine end), run the new one up as you pull the old one out, following the same route (you may have to remove some panels or summat), then fix it to the lever end as you take the old one off.
- You'll probably have to slacken off all the adjusters to make the job easier.
- Try and get the Owners Manual and the Service Manual - Most bikes' manuals are available as free-download PDFs if you look hard enough.
- As you go, take photos on your phone or something, so you know how it came apart and should look when properly assembled.
- Make sure you take the opportunity to lubricate moving parts, including the new cable itself. Not keeping cables lubed often makes them fail.