I was born and raised in a Catholic Family, and was brainwashed to Christianity form prep-school to high school (see my Bio). After I read the Bible several times, I decided to ex-communicate myself with the Catholic faith in particular and Christianity in General.
How did I do it? I just stopped attending anything that relates to Christianity.
And I'm thankful for my Parents and siblings that they accepted my decision. We're still close up to this date.
I'm not saying you do what I do. Do whatever you think will give you peace of mind.
In short, you don't need a process or anything.