First rule of thumb is to not jump straight into any performance enhancements until you take care of any outstanding issues the car may have. Make sure it's running the way it's supposed to and is properly tuned. After that, there are performance chips you can buy which will change the characteristics of engine response, as well as remove the speed limiter and raise the rev limit. To name a few, you can look up Dinan, Conforti, and even Bavarian Autosport has them.