MY GREEN CARD IS EXPIRED BUT I NEED TO RENEW IT. WHAT DO I DO?

You should renew your green card, as it is required by law to have a valid green card to proof your status. If your green card is of the old type with no expiry date, I would strongly recommend you to get the new one. Just fill in the forms and pay the fee. I think it went up actually to around $400. PRICY!!!!