How can I apply for a B2 visa stay extension in the United States?

To apply for a B2 visa stay extension in the United States, you need to submit Form I-539 to the U.S. Citizenship and Immigration Services (USCIS) before your current visa expires. Include supporting documents like a letter explaining why you need the extension, proof of financial ability to support yourself, and a copy of your current visa. It's important to apply well before your current visa expires to avoid any issues.