Permanent Green Cards issued after 1989 usually have 10 year renewal cycles. The expiration date of your Green Card is printed on the front of the card. If your card is expiring, then you can go to the USCIS website (www.uscis.gov) and download Form I-90 (along with its instructions). You should complete the form and return it to the address listed in the instructions manual, along with the filing fee of $370 ($290 Filing Fee and $80 Biometrics Fee*) at least 6 months before the expiration date printed on your Green Card.
If you have a Conditional Green Card and your status is expiring, you should not use the I-90. You must use Form I-751 if you became a conditional resident through marriage to a U.S. citizen or permanent resident or Form I-829 if you became a conditional resident based on a financial investment in a U.S. business.
*Biometrics fee may be waived under certain circumstances so check the instructions before you write your check.