If you are wanting to bring his temperature down, try sponging him with lukewarm water, but if you are concerned about the cause of it and he seems distressed I'd be going to the doctors too. A temperature over 39 degrees is out of the 'normal' range, it could be a response to a tooth coming through or it could be something more serious - it's impossible to know over the internet - not that I'm a trained doctor or anything!

Kerrie