写留学生换课邮件时，应注意以下几个要点：

邮件主题：

确保主题简洁明了，能够准确反映邮件内容，例如：“Request to change my choice of elective course”。

自我介绍：

在邮件开头，应包括你的姓名、学号、专业等基本信息，以便对方能够确认你的身份。

说明换课原因：

简要说明你换课的原因，例如课程难度、时间安排冲突、个人兴趣变动等。

提供具体信息：

明确指出你要更换的课程代码和课程全名，以及新选择的课程代码和全名（如果适用）。

确认更改：

在邮件中表达你希望对方能够确认并更新你的选课信息。

礼貌用语：

使用礼貌和正式的语言，表达对对方时间和帮助的感谢。

落款：

在邮件结尾，使用正式的结束语，如“Best regards,”或“Sincerely,”并附上你的全名和学号。

检查与修改：

在发送邮件前，务必仔细检查语法和拼写错误，确保邮件无误。

```

Subject: Request to change my choice of elective course

Dear Professor [Last Name],

I hope this email finds you well. My name is [Your Name], and I am a student in your [Course Code] class. I am writing to request a change in my elective course selection.

Due to [Reason for change, e.g., a scheduling conflict with another course or a change in personal interest], I have decided to drop the course [Original Course Code and Name] and add [New Course Code and Name] instead. I believe this change will better align with my academic goals and schedule.

Could you please confirm that my new course selection has been updated in the system？ I am grateful for your time and assistance in this matter.

Thank you very much for your consideration.

Best regards,

[Your Full Name]

[Your Student ID]

```

请根据实际情况调整邮件内容，确保所有信息准确无误。