Two options
Remove the ECU and send it to Benchmark Performance, JBS Performance, or Alba Racing for tuning.
Buy a plug-in device, generally a Dynojet/Power Commander 5 is the name, that is programmed....keep in mind that it needs programmed.
The speed limiter needs removed AND the rev limiter raised to get any real benefits. If you just remove the speed limiter it only raises the top speed up a small amount as you will then hit the rev limiter. If you just raise the rev limiter without removing the speed limiter it probably won't make much difference.