Non-immigrant visa holders may apply to extend their stay by filing Form I-539 before their authorized period expires. Extensions are granted at USCIS discretion and require demonstrating continued eligibility and maintaining non-immigrant intent. Visa renewals involve applying for a new visa at a U.S. consulate abroad. Permanent residents must renew their green cards every 10 years, though their status doesn't expire. Naturalized citizens don't need renewals.