If you change the resistor, at least you have to calibrate your Multimeter
But want to do that, do it with the original resistors, so you now where your meter deviates and how much.
So i won`t go into the effort of replacing the resistors.
If you really wan`t a more accurate meter you have to change at least your voltage reference to a better one and or your ADC, but this is not as easy as it seams.
So if you want a better meter the easiest way would be to buy a better one.
As for the analog scale most of them have accuracies about 2%, so calibrating your meter is the best way to improve your measurements.