Renewal requests for Interlibrary Loan items are sent via ILLiad (https://illiad.etown.edu/illiad/logon.html).
Your checked out items are listed in the main menu. Find the item you wish to renew and use the actions menu on the right to select 'Renew.'
Keep in mind that whether or not an item is renewed is up to the lending library. You will be notified via email whether the renewal request was successful, and with a new due date if the request was approved.
Many libraries will not renew overdue items, so make your request before the item is due.