You are probably talking about the 25 GH/s Bitcoin Miner from BF.
I do not know that those have been overclocked. Best place to ask will probably be BF forum. There is quite a lot of discussion concerning modifications and overclocking (concerning Jalapenos at least). I personally have overcloked my Jalapeno from 5 to 8 gh. For that product there is good and easy to follow instructions available.