All history in TNG for this user will stay as is. TES does not have access to TNG to modify anything.
You have to be Level 8 and then you can remove a user as follow:
- Login with your Level 8 login.
- Click User Settings at the top of the page.
- Click "Delete Users" on the Administration page.
- Tick the username that you want to delete.
- Click Apply at the bottom of the page.
You can scroll through the pages using the next page icon at the bottom right of the page.
PLEASE NOTE: the entire call history for this user will be removed.