No worries Kod, welcome....
You will pick many new terms regarding religion that you would have never come across somewhere else. I learned many terms here. So there you go, when one leaves a religion he/she apostates; and if they adopt a new religion they convert. And since Athiesm is not a religion (it's the lack of) so you can not convert to it.
مرحباً بيك في بيتك يا باشا. دنتا نورت
واللهHere is you complimentary parrot, it is a custom around here
![parrot](https://www.councilofexmuslims.com/Smileys/custom/parrot.gif)