Does anyone know how to get criminal charges expunged without a lawyet?

My son is trying so hard to enlist in the Navy but he has a criminal record quite a few years ago. They are sayin now if he can get those charges expunged they'll permit him to enlist. We are poor people and don't own property to borrow on. so I don't see how we can get a lawyer to do this. Does anyone know how to go about getting a record expunged?