I recently turned 18, and my parents know that I don't wish to be a part of their religion.

But the way I did it, is basically what Mithryn is saying. I currently still live in my parents house, i dont leave for college until the fall, so heres what i've learned.

The temptation is huge to lash out when your parents give "hints" or try and guilt trip you into coming back, what you need to do is acknowledge what they say, but decline.

DON'T give false hope, don't lie about what you believe, be frank with them, I understand that some people can't do this because their parents will disown them, etc. But for example when people ask where i'm headed for college next year and i say "OSU" and not "BYU" they freak out, and ask if i plan on serving a mission and i will say "No, i don't plan on it" if they don't respect your choice then they aren't worth the effort. Same applies with your parents

If your parents are open, tell them maybe some things you've learned, I did this and certainly have changed my dad's level of mormonism. He is now somewhat progressive, as in he understands a lot of the past, and the current proof against the religion, but still believes, which is a good forum for discussion.

Just wait it out. It gets better, just be honest and respectful with others and yourself