how to change version number of an App from iTunesConnect with state Prepare for Submission

You can update the version name in a version field in the General App Information area. Screenshot is as below

I have the same problem before.

My solution:

1. Submit the IPA first, status will be changed to "Waiting for Review";
2. Press the red button "Reject the binary" in iTunes Connect, status will be changed to "Developer Rejected";
3. Restart the process again.

---

UPDATE As of 2015, iTunes Connect has updated, allowing users to change version number without uploading any binary.

Go to iTunes --> App store --> iOS App at left side --> Prepare for submission --> General App Information --> Version