What do I need to do to change from Halogen to LED?
The type of driver you need depends on the type of LED bulb you use. Apparently in your country, you can get Constant Voltage LED or Constant Current LED. Choose the matching driver.

Both types of drivers can drive more than one LED. Consult the data sheet for the exact limit.

However, if you have MR16 "fittings" with GU5.3 socket already, it is likely you don't need to replace the existing driver if you purchase Constant Voltage LED rated at 12V. If you have GU10 or screw (edison), that is more likely to be high voltage. That's how it is in the US, I don't know about your country.