just start the car in the normal way i.e put your code in and start the car. then unplug the keypad and right up under the passenger side dash you will find a kinda grey electrical rectangular box. unclip it and unplug it when your car is running straight after you have unplugged the keypad(the plug us under the keypad its self. you wont be able to use the keypad after though! it wont work.
you aint got to fork out any extra cash! i did my conversion last weekend!
just make sure you plug the grey box back in after the conversion or your central locking wont work untill you do! i found that out the hard way