How can you fight a past plea that should have never been entered?

When anyone is assigned a court appointed attorney, that attorney will do whatever it takes to push a case through and not take it to trial. How can you, as the defendant, gain ground to declare misconduct on your court appointment attorney that talked you, a scared kid, into taking a plea for something you know that you weren't guilty of, simply because your court appointed attorney scared you out of taking it to trial to push the case through? Is that even possible? Is it possible to at least get the charge off the books or dropped to a lesser one? Even if the charge is old? It's something that will haunt you for the rest of your life, knowing you did nothing wrong but have consensual sex with a girl who lied about her age and you had witnesses and lie detector tests to prove it, but you were scared into taking a plea. How do you make this ghost go away?