eTicket can be both installed from fresh or upgraded from previous versions of osTicket or eTicket.

Upgrading has been tested with osTicket v1.3.x, but should work from osTicket v1.2 and above without a problem.

NOTICE: Always make backup your files AND database first!

If you ARE upgrading, (backup: attachments, settings.php and automail-settings.pl FIRST), remove all files and folders, upload the new ones, and finally restore any files you backed up.

Then, you MUST follow the upgrade sql upgrade to update the database.
(eg; http://www.yourdomain.com/helpdesk/upgrade.php)