In case anyone else has some problems with doing this upgrade like I did, here's what all I had to do.
As always BACKUP YOUR DATABASE AND CODE. ? (I had to drop database and reupload application several times before figuring this out for two osTicket applications on our servers.)
Download the latest 1.9.x that is stable.
Download the latest 1.10.x that is stable.
Download the latest 1.11.x that is stable.
Upload your existing 1.6 application AS IS.
import your existing database AS IS (if moving to a new server)
Upload everything from the 1.9.x upload folder to start the upgrade process.
Fix any fatal errors that you find in the logs. (I had to fix some call-time pass-by-reference and things like that in the 1.9.x release.
Login to the /scp panel with an admin account and click upgrade. (if it fails repeat 6-7 and fix errors)
If the process was successful, then repeat 7,8,9 for the 1.10.x release and then the same for 1.11.x release.
Hope this helps because I spent a few hours doing this for two different applications.