You can delete the old one and ensure only not expired license are displayed on the Licences Menu when you go on Administrators and the sub-menu "Licences".
Once it's done you should be fine as long as you have as much licences seats than client deployed.
You can also check the Task "Restore licence" in order to have a look on all the licence available. If you see some of them not expired, you can restore them very simply.
Kind Regards,
A. Wesker