I added some user titles in Users & Groups --->> User Titles
But they are not changing according to minimum post i added.
Is there any error?
Try another post or try closing the window then open your forum in new one. I think it's something to do with your forum needs a new visit.
Or go to Admin CP > Tools & Maintenance > Task Manager > Promotion System. And click the little clock on the right to run the task.
Sorry I can't help then, maybe someone else will have an answer.
Go to ACP>Users & Groups>Groups>Registered
Do you have anything in the Default User Title field? If so then remove it. Only if Default User Title is left blank then it will read the custom usertitles that you set, if you have something in the Default User Title field then the custom usertitles won't work.