If you enter Russia without a Russian visa (visa - free entry), you registration will be extended within 25 working days.
If you enter Russia with a Russian visa, you are required to have your visa extended along with the extension of your registration. Extending your visa  usually takes around 45 calendar days. Visa extension costs 1,600 rubles, while visa registration is free of charge. After receiving a new visa, you must immediately apply for a new registration at place of your residence.