Ideally you would open the laptop up and dust off the motherboard itself (especially the processor and video card heatsinks/fans). However, that's a little bit more advanced if you don't know what you're doing, and often involves steps that would void your warranty, which you don't want. So yeah, just the vents should be fine in your case. Cleaning those should definitely solve your problem if they've gotten clogged.

Also, when you get done cleaning, turn your computer on and start playing WoW. After giving it a few minutes to heat up, try to determine whether the fans are working. If you don't hear any fan noise (might need a quiet room) and you can't feel any air being pushed out of the vents, you might actually have a busted fan, rather than a clogged vent. At which point it's time to make use of your warranty, and/or a local computer shop, and/or a nerdy friend who owes you a favor.