After a ticket is created, you can change the Requester of the ticket or Subject or the Description or any of the Ticket Properties from inside the ticket page. Click on the 'More' button within the ticket (details page) to find the 'Edit' button as part of the dropdown.

This would open the Edit Ticket Details page, where you can edit the ticket and save the changes for it to reflect in the ticket. 

If you are using Freshdesk on Mint, you will find the 'More' option against the subject of the ticket. Clicking here will give you an option to 'Edit' the details of the ticket.

Note: This option would not be visible if the ticket is an Outbound Email, i.e. 'Source' is Outbound email.