How to Rename package in Android Studio

1. In your Project pane, click on the little gear icon.
2. Uncheck / De-select the Compact Empty Middle Packages option
   
3. Your package directory will now be broken up in individual directories
4. Individually select each directory you want to rename, and:
   • Right-click it
   • Select Refactor
   • Click on Rename
   • In the Pop-up dialog, click on Rename Package instead of Rename Directory
   • Enter the new name and hit Refactor
   • Click Do Refactor in the bottom
   • Allow a minute to let Android Studio update all changes
   • Note: When renaming com in Android Studio, it might give a warning. In such case, select Rename All
   
5. Now open your Gradle Build File (build.gradle - Usually app or mobile). Update the applicationId in the defaultConfig to your new Package Name and Sync Gradle, if it hasn't already been updated automatically:
   
6. You may need to change the package= attribute in your manifest.
7. Clean and Rebuild.
8. Done! 

https://stackoverflow.com/a/29092698/4964308