If you wish to visit the U.S. for a short duration, you will need a visitor (B-2) visa. This visa allows you to spend a limited time in the U.S. for pleasure, tourism, or medical treatment. This includes recreation and visiting friends or relatives.
When you enter the U.S. with a B-2 visa, you will receive an I-94 card that will be stamped by an immigration officer. This stamp will indicate the length of your authorized stay in the United States.
If you wish to extend your stay as a visitor past the date indicated on your I-94 card, you will need to file an application with USCIS (U.S. Citizenship and Immigration Services). This application is filed on Form I-539, Application to Extend/Change Nonimmigrant Status. You should file this application before your current period of authorized stay expires.
When completing Form I-539, you will be required to provide personal information, including your name, address, and date of birth. You will also need to indicate how long you wish to extend your stay and describe how you are supporting yourself financially while you are in the U.S.
In addition to Form I-539, you will need to provide a written statement explaining in detail your reasons for requesting an extension of your B-2 status. Explain how your reasons for staying in the U.S. remain temporary and provide proof of your plans to depart the U.S. when your extend stay expires (a copy of your plane ticket, for example).
USCIS has discretion to grant or deny the application, so you should make all efforts to present your reasons as clearly and completely as possible. Provide as much supporting documentation as you can regarding your purpose for being in the U.S., the reason for the extension, your ability to support yourself financially, and your intention to return to your home country at the end of your authorized period of stay.