Those visitors who wish to stay beyond the time indicated on their Form I-94 (link to I-94) must contact the Department of Homeland Security’s Bureau of Citizenship and Immigration Services to request an application to extend status. The decision to grant or deny a request for extension of stay is made solely by the Bureau of Citizenship and Immigration Services.

Total stay allowed is 1 year including a six month extension. 

Learn more about Extension of Stay vs. Visa Expiration
Path2usa Resource: Visitor Visa Extension
USCIS Resource: How Do I Extend My Stay in the United States?