B2 - Visitor Visa Extension Process

Here you have to register an account and then file for extension by logging in

https://efiling.uscis.dhs.gov/efile/

Here is more information : http://www.path2usa.com/usa-visitor-visa-extension

Documentation you need to mail to USCIS :

·       Letter for reason to extension request.

·       Copy of I-94 Arrival/Departure Record, valid through

·       Copy of passport front-back and visa pages.

·       Copy of return airline tickets 

·       Affidavit of Support (Form I-134), and bank statements.