When the classes are imported, the system creates resources for each teacher. A resource is an object that holds the slots, or classes. The resource is given a name from the teacher's contact record in the form "first last", and the room is copied onto the PTA resource. Once the resource has been created, changing the teacher's name or room either by editing it from the contacts tab or by re-importing the corrected teacher file, will not affect the resource name or room. The resource name is what is shown on the reports and to the parents. If there are a few errors with spellings or room changes, it is easy enough to alter the information from the Admin UI. (see: Modifying Teacher or Room Data) If the teacher data is all messed up, then it is easiest to delete the events and start over.
When importing the classes, the system takes a look at what teacher each class should go on. It uses the TeacherID to look for an existing resource, if there isn't one it will create the resource in the Slot Editor and Appointment tabs and then it will put the class on that resource. Importing the classes makes the system copy the teacher's name. Once that copy happens, changing the teacher's contact information will not alter the resource name.
See Modifying Teacher or Room Data to change the spelling of a teacher's name.
Take a look at Modifying Teacher or Room Data to see how you can change teachers and reassign classes.