If you are an Admin in MCA Suite, you can delete users from your system.
To delete users:
1. Navigate to the Admin User screen
2. Search and select a user
3. Click 'Inactivate'
After this, you still have a chance to reactivate the user but they will not be able to login.
To completely remove the user from the system go back to Admin > User and click Purge All Inactive Users.