1.8 16v gasoline, automatic: replace throttle flap?

Moin. On the net I read “Exchange a rosary flap, very easy, you can also as a layman”. But now I stand there and still don’t know how to do it…. I have a Laguna 2 2002 GT. Does anyone have a guide on what and how to do it? I am grateful for every advice. Greetings