Você precisará (lista completa aqui ):
Você pode se inscrever on-line ou por e-mail e eles recomendam que se inscreva pelo menos 45 dias antes da sua estada expirar.
Observe que seu visto atual ainda deve ser válido. Caso contrário, você precisará solicitar um novo, citando CIS :
If you want to extend your stay in the United States, you must file a request with U.S. Citizenship and Immigration Services (USCIS) on the Form I-539, Application to Extend/Change Nonimmigrant Status before your authorized stay expires. [...]
You may apply to extend your stay if:
- You were lawfully admitted into the United States with a nonimmigrant visa
- Your nonimmigrant visa status remains valid
- You have not committed any crimes that make you ineligible for a visa You have not violated the conditions of your admission
- Your passport is valid and will remain valid for the duration of your stay