Purchase the LCI headlights
Purchase the FRM3 (foot well module)
Code the car (change the order date and code the FRM)
Thats it. If you want the coronas to dim when the lights are on, you will need to run one additional wire from the FRM to the headlight.
<edit> I just realized that you said you had the halogens
I think that the wiring is different and you will need to move some wires at the connector. Your best bet would be to look in WDS to see what the pinout differences are between the xenons and halogens