Not difficult to drop any of it.
I never felt I really adopted any of it in the first place, although I tried as a kid.
It just didn't stick.
I'm not sure which ideas of religion I dropped first, but over time it was easy to drop it all until I could finally say I was atheist. My remembrance of it was that I once believed and wanted to be a minister, but once I discovered there is nothing to it, I felt betrayed. I still do. I feel betrayed by the adults that brought religion to me and they are believers because their parents did the same with them. I feel those who are the most upset on ideas of atheism are that way because they don't want to admit they were fooled.
Some want to tell me that I am wrong and they start making up more crap to prove it. All I know for sure is that our world of religious writing in no way reflects feelings or words of any creator being. People that think otherwise wanted to believe in the first place and they just keep on making more stuff up.
I have no more proof one way or the other on these matters but I do not have doubt revolving around some ancient writing. There is no proof that gods are trying to contact you.
What a great question! I grew up in a reformed tradition (PCUSA) and was always encouraged to question things. I understood some things for the same reason I embraced Christianity -- almost everyone around me did as well. So evolution and a 14 billion year old universe were never at odds with my faith. Hell was also at least called into question as many family friends and fellow church members claimed no loving God would send anyone to such a place.
One of the first things I remember questioning was the idea of eternal life. If life was a gift from God, wasn't one, temporary, earthly life gift enough? Why did life have to go on forever?
As I grew older (some still question whether I have ever grown up) I began to question cherry-picking. Why was a loving god embraced and a wrathful, vengeful god rejected? Was it because one "felt right" and one didn't?
The last idea for me to drop was the idea of a deity. Once I had dropped everything else (The universe didn't require Him. The origins of life and consciousness didn't require Him.) "God" was just this extra, poorly-defined thing.