Switching between three output voltage settings on a switching regulator
I answered a similar question a while ago. I recommend using FETs and wiring the resistors in series to make the circuit 'fail-safe'.
See here: Changing output voltage of a buck converter by electronically swapping the feedback resistors
You can also use mechanical switches, but I recommend using debounced signals to control the FETs so that the voltage transitions are smooth.
A fancier method would be to use I2C and a current-setting DAC like the DS4422. Then you can have precise control over the voltage and its slew rate.
Any of these techniques apply to switching or linear regulators that have a feedback pin, even modules.