To delete a user from Teamtailor, head over to the Employees section (1), and go to the user you want to delete. Click Settings (2) and scroll down to the button of the page. Here you will find Delete employee (3). Click it to delete the user.
If the user is listed as the recruiting manager for any jobs, you will need to assign that role to another user. You will get a dialog box where you can do this right away.