How to change colour of the angel eyes in bmw e39?

i have a bmw 2001 e39 and i wanted to change the colour of the angel. but not sure how it is done. do i change just the bulb or the unit?|||well you can buy one from ebay and instal it..... but its hard to instal it its betther if you give it to a pro... here is the link go there|||its a ring wrapped around the headlights but i say it probaably almost impossible to replace that with a diffrent since its so hard putting them in