A conditional green card is issued to a conditional permanent resident and is valid only for 2 years. You cannot renew such card, only to apply for removal of conditions on the card. A conditional permanent resident must file a petition during the 90 days period before the card expires. For this purpose, use Form I-751 or Form I-829 depending on your case.
If your conditional residence is based on your marriage, then you must file Form I-751, Petition to Remove Conditions on Residence. It is a joint petition, meaning that you and your spouse have to file it to USCIS together.
If your conditional residence is based on a financial investment in the United States, then to remove the conditions on your permanent resident status you must file Form I-829, Petition by Entrepreneur to Remove Conditions.
Upon successfully removing conditions on residence, a permanent resident (along with any children that filed on the same petition) will become lawful permanent residents with a 10-year green card. This card also expires but the status granted cannot expire.
If you do not file Form I-751 or Form I-829 as required, you will automatically lose your conditional permanent resident status as of the 2nd anniversary of the date you were granted conditional status. As a result, you will become deportable from the USA.