To extend your B-2 tourist visa while in the United States, you must file Form I-539, Application to Extend/Change Nonimmigrant Status with USCIS. You should apply at least 45 days before your authorized stay expires, as indicated on your I-94 arrival/departure record. Along with the form, submit supporting documents such as proof of financial support, reasons for the extension, and evidence that you intend to return to your home country.