How to convert a range of 0.5 to 4.5V for a range of 0~3.3V? ACS712 20A current sensor
If your outputs are low-impedance or buffered, than you can use a differential amplifier. A basic schematic is the following,


The transfer function maps 0.5 to 4.5 to 0 to 3.3. Though I would suggested limiting the output swing a few 100 mV above/below the rails.



Edit: Showing thevenin of ADCREF/2, Scale resistors as needed.