There are two ways to upgrade from college English to undergraduate English. The first is full-time general higher education. To apply for full-time general higher education, you must apply for it in junior college, and you can't apply for it after graduation.
The second is adult education, including adult self-study, adult college entrance examination and online education. There are fewer restrictions on entering adult education, and you can take exams after work. Generally speaking, study time is relatively free.