There are basically three traditional ways to get out of college courses. All three involve taking a test that shows basic competency in the course material. Many high school students are familiar with AP (Advanced Placement) courses. You take a course in high school, then at the end of the school year, you take the AP test, and if you score high enough on it, you get college credit.
The main problem with AP courses is that they are only available to high school students. Once you've graduated, it's too late. Another problem is that it takes a whole school year to get your credit. This is where CLEP (College Level Examination Program) and DSST (Dantes Standardized Subject Tests) come in.