Yes you can change the Lawyer anytime. Please make sure you have all the copies of your documents with you. If you have your labor certification done rest I 140,I485, I 765, I131 can be done by your self. I am with immigration law firm based in virginia pls call me for free consultation at 703 8488855 or 703 6262769 email at akatwalifegood@aol.com. If your labor cert. is done then your major hurdle for PR is passed, wish you a good luck.