We'd suggest swapping the bulbs over, not the ballast. The standard Renault ballasts are a nightmare to get to (usually hidden underneath the headlamp surround etc).
Pull the bulbs out, swap them over, see if the culprit one fires up. It's not a fantastic job, but it'll be a lot easier than changing the ballasts over.
Just a quick note; we also suggest changing a pair of bulbs at a time, rather than just one, because the brand new bulb wont be exactly the same colour as the old one, for obvious reasons, so it's better to replace the pair.
Hope that helps.