If you accidentally invite the wrong person to your class, you are able to rescind the invitation before they join. However, if they enroll. you can still remove them. You can also remove administrators, if needed.
To remove a participant
Go to the 'Participants' tab and find the student or administrator you wish to remove. Click on the 3-dot icon and then "Remove from Class." You will be asked to confirm.
If the student has class content (such as discussions and posted work), it will NOT be deleted.
Please note: A class must have an instructor associated with it, and therefore you cannot simply delete the instructor. You can change the instructor. The original instructor will become an administrator, which you can delete as noted above.