Welcome, vrrmz !
You mean about lowering the top gear RPM? We've had a couple of other owners wondering what could be done. You could install larger diameter tires, which would help a little, but would also throw off your speedometer/odometer a bit.
Play with a calculator like this...
http://www.wallaceracing.com/calc-gear-tire-rpm-mph.php
It's possible there's a different 5th gear set that could be swapped in this transmission. It may actually be a fairly simple mod (5th gear lives under the stamped steel cover on the end of the transaxle). The hard part would be finding a compatible gearset from another Nissan that would fit.
On the other hand, you'll get used to the RPM. Lots of owners have taken their Micras on long distance highway trips with no complaints. Thread:
Is Micra suitable for high speed highway driving, long distance