I definitely agree with Aaron in that it probably depends on why you think the teacher is 'bad,' whether its because of a clash of teaching/learning styles, or something more serious or due to a lack of effort. I would:
- Go to your teacher in the first instance and identify for them what it is you believe is missing from their teaching. Are they not explaining things well enough for you? Are they not giving you enough work at home? Too much? Talk to them - Teachers are human beings and a lot of the time them being aware of the issue is enough to fix it.
- If this is unsatisfactory for you, talk to your year coordinator/similar person about the circumstances. Again, doesn't have to be hostile, "I don't feel I am learning much in this class and this is why."
Depending on how this second step goes, you could politely request to be moved - But I doubt they would do it for you unless you try to resolve the issues with your current teacher first. That is almost always easier anyway

It is absolutely your right to have a teacher that is doing their job effectively and properly, but sometimes even when teachers do this it just doesn't quite click. Lots of different teachers and lots of different learning styles make this inevitable. It's just about communicating the issues so those inconsistencies can be fixed, it doesn't have to be a bad experience
