Do it as soon as possible. It's simple and you can do it online. There is a section on the application which asks you for the schools that you want to have your scores sent to, so be prepared to list those you are interested in. Also, once you have submitted this list, you cannot ammend it, meaning you cannot go back and change a school. If you change your mind you will have to pay another fee and have your scores submitted to the new schools. Best of luck!