Engine compartment driver's side fender. You'll have to remove the battery to get at it. It's that silver box on the fender.

 

You would not want to remove the rev limiter even if you could, because that is how motors start throwing their guts through the hood. The limiter is there for several reasons and all of them are good reasons. You best performance gains, as well as higher rev limiter, is with the A/FX PCM.