Sounds similar to my kit differing in the controller brand alone, first place i landed looking for controller info was pedelec.de where some controller gurus have alternative f/w for some controllers possibly yours? but not mine.
Generally speaking the option to change voltage would only apply where the controller is able to handle both voltage input range levels. if your employing a 36v controller its not going to have the 48v option.
As for changing any settings or parameters on my controller all i can mod is the speed metric and wheel size, i can also reset distance counters and change pas level on the fly but most system config is simply disabled.
if a problem an alternative KT controller that can fit under the battery slide could be sourced to replace yours providing a full range of configurable parameters that can actually change the way the bike works, not just lifting the speed limit but changing how power is delivered (if of interest its worth looking into)
However after a week on the bike any urgency may also disappear for any such project like it did this end..
Neither my bike or its brakes could cope with speeds greater than 16mph considering my mass and whats usually on the back of the bike. so meh..
fwiw once the ebike honeymoon was over i tend now not to use the e-power at all heading off (downhill and flat mostly) engaging when i feel like it at level 4 - 5 depending on rd conditions 15mph without suspension can be VERY bumpy on some rds. I rarely use levels 1,2,3, or the throttle which will only work to 4mph (f/w limitation again).
the extra £80-90 for the controller/headset switch would enable features but meh, the bike works as is
btw keep an eye on your front brake and its wear..