Even if there is a software setup to change the limits, you'd need to get the software (and possibly cable) from the manufacturer of the bike, or the dealer, for that model (and year) of that bike. There's no generic software for this stuff. Not all that likely they'll provide this, for liability reasons if nothing else.
Some systems have a limit setting in their display menus; you'd need to check your manual for that. If there's nothing in the manual about it, it's probably locked out for legal reasons in your locale, and probably can't be bypassed without something from the dealer or manufacturer (or is actually in the hardware programming from factory and not alterable regardless). There might be a dealer service menu with the setting, but you'd need to get info from them on how to access it (password, special button sequence, etc). It's not very likely they'll hand out this info, either.
To know if there is a limit or not, or if it is simply not capable of faster speeds, put the bike upside down (or otherwise with the powered wheel off ground, and run the motor at it's fastest speed.
If it goes exactly as fast as it does when riding it, then there is a limiter in play. How fast it might be able to go when not limited will be determined by the motor winding, any gearing (internal or external to the motor) between motor and wheel, wheel diameter, system voltage, and system current.
If it goes slightly faster (a few percent) offground than riding it, there is no limiter, it's just not capable of going any faster, and you'd need to replace parts to get a higher speed. That could include the motor, battery, and controller/display set. (replacing the controller/display may also change how other things on teh bike work, or make them not work at all, like throttle, pedal sensors, etc, depending on what you replace them with since not all controllers have the same functions or capabilities).
