Migrating to Unity5
If you haven't used Android Native with the previous Unity versions, you have nothing to worry about, no additional actions required, you can just Install the plugin.
If you switched your project to the Unity 5+. Make sure you have Ultimate Mobile v3.2 or higher.
Open plugin Settings and click Reinstall button under the Actions menu. As showed on the screenshot bellow
If you building for IOS, Please read IOS Migration Guide as well.