Need basic step-by-step instructions for W201 euro installation

I don't know if I can do this on my own...now thinking about paying someone to do it. I've been hearing that installing euros is a simple job. I'm sure it is and I want to do it myself. But the problem is that I have no reference point, like what to do first, second, and so on. I guess first things first, DO I NEED TO UNPLUG THE BATTERY TERMINALS? If yes, which wire first, positive? And what is the next step? Need help! Thanks!