Deleting a user
Has someone left the company or taken up other responsibilities? Contact the Administrator of your account, he has access to all plans and can delete users on account, plan or project level.
When you delete a user, his related activities won't be deleted. And the activity log stays intact, so you know what happened before. So there's someone else who needs to take ownership of projects, tasks, …
Contact Support if you just want to change the email address, for instance, if someone else takes over.