This is done with the same kind of amplifiers or resistor networks as you might use with AC voltage. For example, you might attenuate a DC voltage useing a resistive divider, or if you want to maintain a specific source or load resistance you could use a T-pad configuration. Ohm's law works the same with AC or DC.
When amplifying DC, there are some additional things to be careful of that don't occur with AC amplification. The first is that with simple transistor amplifiers, the quiescent operating point may drift due to temperature effects such as the variation of DC current gain with temperature.
One can use op-amps to amplify DC very effectively with little more trouble than with AC amps. Many novices run into problems when using a single power supply in an op-amp based DC amplifier, so it is often easier to work with postive and negative supplies in such circuits and reference everything to ground.