At most colleges, students can jump in and try a course for a week or two to see if they like it. If they decide they don't want to take it for any reason, they can "drop" it, meaning they officially drop out of the class. As long as they do so within the specified limit of the trial period, there are no negative ramifications on their academic records.
It might be worth asking your counselor if your high school has a policy like this (or if a counselor/teacher might allow you to avail yourself of it). For example, if you're picking classes for next year and you're unsure about AP Chemistry, honors trig, or whether you can really handle an extra class before school, ask your counselor if it's possible to drop the class within a limited time without hurting your record. If you can, jump in with reckless abandon and see what happens.
It's much better to ask about the option before you begin the course, rather than asking once you get a C- on your first exam.