Problem in updating app on iPad

I created an app for iOS 3.2 for the first version 1.0.

Recently I created an updated app for iOS 4.2 with print feature etc. for the second version.

My problem is that, the users are not able to update the app from appstore.

They are facing issues like data loss of version 1.0 app, crashing etc.

Can someone explain me what can be the reason for this?

And, how can I test this thing on my device, as I am not having the version 1.0 app from appstore, but the code for both versions.

Delete your new one on your test device and install the old one. Then build and debug the new one line by line. I had lots of trouble my first time through due to confusion over the update/migration process of core data. If you use core data, chances are your existing customers have an out of date store DB that your new code is crashing on. The store doesn't get wiped in an update if it's in your user's document directory... Only the one in the app bundle. You'll need to handle that reset or tell core data to migrate it to the new model. Of course, all this is speculation since you've given almost no details about the problem, frameworks used, log files, etc.

During a normal install process, data should not be overwritten. NSUserDefaults and files should remain during an upgrade, as long as the user doesn't delete the app first. I assume the crashing occurs after the new version is installed?