That's probably the #1 question people ask. Officially, no, there's no way to make your NIU running faster - the EU model is limited to 45km/h (or even 25km/h) which is the EU law for this kind of vehicles.
That said, the motor and battery are definitely capable of delivering higher speeds. Some videos from China prove, that this is possible. Have a look at those videos here or here. Obviously driving faster will drain the battery faster, too.
What they do is using a 2nd, aftermarket motor-controller in parallel to the original one. Here's the post about this tuning.
Depending on your NIU model, you might give these eastereggs/hacks a try... more recent 2017 N1s models won't change their limit with these.
I think you can imagine yourself that you would void your warranty as well as risking to get into serious trouble with your local police/insurance in case of an accident.