As a general rule, I don't delete students from WebCT unless asked. Here's how you can remove students from a WebCT course yourself:
1. Once inside your WebCT course, click on Control Panel in the upper left.
2. Click on Manage Course.
3. Click on Manage Students.
4. Click on a student's name.
5. Click "Delete".
6. WebCT will ask you to confirm, and after you say yes, then the student has been removed from the course.