As a nonimmigrant you temporarily enter into the U.S. for a specific purpose such as business, study, temporary employment or pleasure. When you enter into the U.S., a U.S. official assigns you a nonimmigrant category according to the purpose of your visit. If you want to change the purpose of your visit while you are in the U.S. then you or, in some cases, your employer must ask the United States Citizenship and Immigration Services (USCIS) to change your nonimmigrant status.
Note: For instance, if you arrived in the U.S. as a tourist, but want to become a student, you must submit an application to change your status with the USCIS. If you do not apply to change your nonimmigrant status, you will be violating U.S. immigration laws.