You can only delete users who have no timesheets, no time off bookings, and no expenses in the system. If an employee has left your organization or has gone on leave, consider disabling them instead of deleting them.
Disabling a user prevents them from accessing the system, but allows you to retain their historical data. All of the user's license seat assignments are removed when they are disabled.
To disable a user:
Select Administration from the top menu, and then select Shortcuts > Users from the side menu.
Select the Users tab or the External Users tab, as applicable.
Click the edit icon next to the name of the user you want to disable, or double-click their name.
On the Access tab, in the Login section, enable the Disable Login check box.