As @rubycon mentioned in [this post][1], Read the documentation: [Publishing Updates on Android Market][2]
> Before uploading the updated application, be sure that you have incremented the android:versionCode and android:versionName attributes in the <manifest> element of the manifest file. Also, the package name must be the same and **the .apk must be signed with the same private key. If the package name and signing certificate do not match those of the existing version, Market will consider it a new application and will not offer it to users as an update.**
[1]: https://stackoverflow.com/a/4843261/3048424
[2]: https://developer.android.com/guide/publishing/publishing.html#marketupgrade
Nothing. Read the documentation: [Publishing Updates on Android Market][1]
> Before uploading the updated application, be sure that you have incremented the android:versionCode and android:versionName attributes in the <manifest> element of the manifest file. Also, the package name must be the same and **the .apk must be signed with the same private key. If the package name and signing certificate do not match those of the existing version, Market will consider it a new application and will not offer it to users as an update.**
[1]: http://developer.android.com/guide/publishing/publishing.html#marketupgrade