1. Direct expression: Explain directly to the teacher why you don't want to continue the calligraphy class. You can say that you are not interested in calligraphy, or you have other interests that you want to pursue more.
2. State your concerns: If you feel that it is inappropriate to refuse directly, you can tell the teacher your concerns. For example, you can say that you are not adapted to the current curriculum, or that you have mastered the content of calligraphy class very well and don't need to continue studying.
3. Give other reasons: You can give the teacher another reason, for example, your family's financial situation does not allow you to continue paying tuition fees, or you have taken other courses and don't have enough time and energy to continue taking calligraphy classes.
4. Try to negotiate: You can try to negotiate with the teacher to see if you can provide some flexible curriculum arrangements, such as reducing the frequency of classes or changing the class time.
Whichever method you adopt, you should be honest and polite. The teacher will understand your thoughts and thank you for your honesty.