Video by Vespa Portland via YouTube
Source
How to unlock a NIU scooter to achieve a higher top speed.
1. Hold the green button while the scooter is OFF
2. Use the key to turn the scooter ON
3. Immediately pull the right brake lever and hold for 3 seconds, then release the brake lever and the green button at the same time
4. Press the green button for 10 seconds
5. Release the green button and pull the brake lever for 1 second