What I was doing till now, whenever I want to give my plugin to QA team for testing, I used to tell them that uninstall the previous 1 and intsall the new one. Because I was not having time (so many bugs was there in existing plugin) to do R&D on upgrade API.
But now I have to stop the data loss.
Now finally I have started reading upgrade API, but I just understood from that is, We have to change version in version.php and add new file in db folder as upgrade.php
But what to write in that file, Please help ASAP