Hello. Usually, American universities require to transfer credits, and they must reach the minimum credits. For example, some universities require that the credits before transfer should not be less than 24, and each school is different. Go to official website, the school you want to transfer to.

In addition to credits, you need GPA, and generally you don't need SAT. However, if your credits are not up to standard or you have special requirements, you still need to provide SAT scores. The other is the transcript of the original university, the official transcript of high school, and the course description.

If it does not involve changing majors, general credits can be transferred. Most students transfer from freshman to sophomore, and they all study general education, so it is more convenient to transfer. It is easier to transfer from a good school to a slightly worse school, but it is more difficult to transfer to a good school. Usually, GPA is very demanding.

I hope I can help you and wish you success in your studies!