Can somebody answer me can I make some updates on my app after I had uploaded the app in AppStore, and can I update the app such that there would be in-app purchase if it was not before I updated?
Updating is fairly straight forward. Go to the comment page and select + icon like you did the first time. This time, however, just add the new version number. See pict.
Then simply upload the new build and follow all the same things you did when you first uploaded version 1.
All my app are free, so not sure about adding in-app purchases. Someone who know will be along.