The second question is that, generally speaking, the application condition for graduate students to apply for universities should be to pass topik4, but the chances of winning advanced courses are definitely higher. English is also very important to apply for Korean graduate students. Korea compares any TOEFL and TOEIC. You can prepare for these two exams if you have time. If the level of Korean is not good, you can study English well and apply for English teaching, but the tuition fee for English teaching will be slightly higher than that for Korean teaching. Moreover, Koreans will feel awkward and difficult to understand when they speak English at first. It is suggested to learn Korean well and apply for Korean teaching. English can be tested to prove your strength.
Third, there are many materials to be prepared for applying for graduate students, but they are somewhat different according to the admission conditions of each school. But basically, you have to apply for a passport and visa, a deposit certificate of about RMB 654.38+million, a guarantor's employment certificate and financial certificate, an application, a university research plan, various awards and achievement certificates. These are the most basic.
Finally, you can change your major in Korea, but if it is a cross-major, you may have to study part of the undergraduate course at the postgraduate stage and take credits with the undergraduate course, which varies according to different schools.
When you have time, you can go to official website of various schools to look at the enrollment brochures, which is very clear. Don't worry, take your time ~
I said a lot, I hope it will be useful to you! Come on!