check out following link:
https://egov.immigration.gov/crisgwi/go;jsessionid=a9NA-QxF2ix5?action=coa
You must file AR-11 by law but don't have to change your address on i-485 petition. keep the copy of your ar-11 or confirmation info if file on line.
i changed my address 8 month ago both paper and online, but they still sent mail related to i-485 to old address.