If you are already in the U.S. under another valid immigrant status you might be eligible to change your condition.
It is essential to submit your application to the USCIS as soon as you determine that you need to change your visa category. Moreover, you must file your request before your authorized stay expires. If your application is rejected, you will need to go back to your home country and submit a new request.
If you live in a foreign country you must apply for a B1 Visa in your country of residence.
First of all, you need to complete an online Form DS-160 (Online Nonimmigrant Visa Application). If the USCIS approves your petition, you will be asked to attend an interview. This will take place at your local U.S. Embassy or Consulate.
The cost of a B-1 visa is $160, plus an issuance fee depending on your nationality.