Upgrade and Versioning of your apps

If you have developed feature or bug fix your Android apps, you have to change the version of your app, before you can upload it to Google Play.

versionCode - Integer only. That's the version of your application code. You must change (normally +1) its or Google Play will not allow you upload the APK.

versionName - String. Version name that all users can see. So that they can identify which version they are using. (normally in format like 1.0.2)

See more in Android Developer - Versioning Your Applications