If your computer is still under warranty apple will replace the battery for you for free if it is swelling.
They may even replace it out-of-warranty if it is swelling. Apple and most other manufactures are very sensitive about battery and power adapter issues, especially those that might have fire, smoke, or sparks involved.
I took a swelling battery which was way out of warranty into a Apple Store, and the Genius told me he couldn't let me leave the store with that battery! He exchanged it for a new one.