how to change sexual thinking? sexually attracted to mud

I know this sounds weird but I want badly to correct it but I seem to be sexually attracted to mud. Like when I see pics of it or see comics or cartoons of it I get an erection. And sometimes, I get wet dreams thinking about it. However, i want to be sexually attracted to girls/women but I can't get stimulated when I think about girls. How can i change my sex characteristics to be attracted to women?